Methods of fabricating MEMS devices having overlying support structures

ABSTRACT

Embodiments of MEMS devices comprise a conductive movable layer spaced apart from a conductive fixed layer by a gap, and supported by rigid support structures, or rivets, overlying depressions in the conductive movable layer, or by posts underlying depressions in the conductive movable layer. In certain embodiments, portions of the rivet structures extend through the movable layer and contact underlying layers. In other embodiments, the material used to form the rigid support structures may also be used to passivate otherwise exposed electrical leads in electrical connection with the MEMS devices, protecting the electrical leads from damage or other interference.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/490,880, filed on Jul. 21, 2006, now U.S. Pat. No. 7,566,940, whichclaims priority under 35 U.S.C. §119(e) to U.S. Provisional ApplicationSer. Nos. 60/701,655, filed on Jul. 22, 2005, and 60/710,019, filed Aug.19, 2005, each of which is hereby incorporated by reference in itsentirety.

BACKGROUND OF THE INVENTION

Microelectromechanical systems (MEMS) include micro mechanical elements,actuators, and electronics. Micromechanical elements may be createdusing deposition, etching, and/or other micromachining processes thatetch away parts of substrates and/or deposited material layers or thatadd layers to form electrical and electromechanical devices. One type ofMEMS device is called an interferometric modulator. As used herein, theterm interferometric modulator or interferometric light modulator refersto a device that selectively absorbs and/or reflects light using theprinciples of optical interference. In certain embodiments, aninterferometric modulator may comprise a pair of conductive plates, oneor both of which may be transparent and/or reflective in whole or partand capable of relative motion upon application of an appropriateelectrical signal. In a particular embodiment, one plate may comprise astationary layer deposited on a substrate and the other plate maycomprise a metallic membrane separated from the stationary layer by anair gap. As described herein in more detail, the position of one platein relation to another can change the optical interference of lightincident on the interferometric modulator. Such devices have a widerange of applications, and it would be beneficial in the art to utilizeand/or modify the characteristics of these types of devices so thattheir features can be exploited in improving existing products andcreating new products that have not yet been developed.

SUMMARY OF THE INVENTION

In one embodiment, a method of fabricating a MEMS device, is provided,including providing a substrate, depositing an electrode layer over thesubstrate, depositing a sacrificial layer over the electrode layer,patterning the sacrificial layer to form apertures, depositing a movablelayer over the sacrificial layer, forming support structures overlyingthe movable layer and at least partially within apertures in thesacrificial layer, and etching the sacrificial layer to remove thesacrificial layer, forming a cavity between the movable layer and theelectrode layer.

In another embodiment, a MEMS device is provided, including a substrate,an electrode layer located over the substrate, a movable layer locatedover the electrode layer, wherein the movable layer is generally spacedapart from the electrode layer by an air gap, and wherein the movablelayer includes depressions in support regions, and rigid supportstructures formed over the movable layer and at least partially withinthe depressions in the movable layer.

In another embodiment, a MEMS device is provided, including first meansfor electrically conducting, second means for electrically conducting,and means for supporting the second conducting means over the firstconducting means, wherein the supporting means overlie portions of thesecond means for electrically conducting, and wherein the secondconducting means is movable relative to the first conducting means inresponse to generating electrostatic potential between the first andsecond conducting means.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view depicting a portion of one embodiment of aninterferometric modulator display in which a movable reflective layer ofa first interferometric modulator is in a relaxed position and a movablereflective layer of a second interferometric modulator is in an actuatedposition.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device incorporating a 3×3 interferometric modulator display.

FIG. 3 is a diagram of movable mirror position versus applied voltagefor one exemplary embodiment of an interferometric modulator of FIG. 1.

FIG. 4 is an illustration of a set of row and column voltages that maybe used to drive an interferometric modulator display.

FIG. 5A illustrates one exemplary frame of display data in the 3×3interferometric modulator display of FIG. 2.

FIG. 5B illustrates one exemplary timing diagram for row and columnsignals that may be used to write the frame of FIG. 5A.

FIGS. 6A and 6B are system block diagrams illustrating an embodiment ofa visual display device comprising a plurality of interferometricmodulators.

FIG. 7A is a cross section of the device of FIG. 1.

FIG. 7B is a cross section of an alternative embodiment of aninterferometric modulator.

FIG. 7C is a cross section of another alternative embodiment of aninterferometric modulator.

FIG. 7D is a cross section of yet another alternative embodiment of aninterferometric modulator.

FIG. 7E is a cross section of an additional alternative embodiment of aninterferometric modulator.

FIG. 8 is a top view of an array of interferometric modulator elementsin which the individual elements comprise support structures.

FIGS. 9A-9J are schematic cross-sections illustrating a method forfabricating an interferometric modulator element comprising supportstructures located over a movable layer.

FIG. 10 is a schematic cross-section illustrating an interferometricmodulator element fabricated by the method of FIGS. 9A-9J wherein thesupport structures have been made thicker.

FIGS. 11A-11G are schematic cross sections illustrating certain steps ina process for fabricating an interferometric modulator having inorganicpost support structures.

FIGS. 12A-12D are schematic cross-sections illustrating a method forfabricating an interferometric modulator element comprising supportstructures located both above and underneath the movable layer.

FIGS. 13A-13E are schematic cross-sections illustrating a method forfabricating an interferometric modulator wherein a portion of aphotoresist mask is utilized to form a substantially planar surface onwhich a movable layer is fabricated.

FIGS. 14A-14C are schematic cross-sections illustrating steps which maybe performed to selectively remove portions of a reflective layer priorto forming movable and support structures.

FIGS. 15A-15C are schematic cross-sections illustrating alternativesteps which may be performed to selectively remove portions of areflective layer prior to forming movable and support structures.

FIGS. 16A-16B are schematic cross sections illustrating certain steps ina process for fabricating an interferometric modulator having an etchbarrier layer which protects the sacrificial material from an etchingprocess which forms inorganic posts.

FIGS. 17A-17B are schematic cross sections illustrating certain steps inthe fabrication of an interferometric modulator having an etch barrierlayer which isolates inorganic posts from sacrificial material.

FIG. 18 is a schematic cross section illustrating a partially fabricatedinterferometric modulator wherein an etch barrier layer, which isolatesinorganic posts from sacrificial material, is partially removed.

FIG. 19 is a schematic cross section illustrating a partially fabricatedinterferometric modulator wherein a post structure is used as a hardmask to remove a portion of an etch barrier layer.

FIG. 20 is a schematic cross section illustrating a step in thefabrication of an interferometric modulator in which an adhesion layersecures a support structure to a movable layer.

FIG. 21 is a schematic cross section illustrating a step in thefabrication of an interferometric modulator in which a protective layerisolates a rivet structure.

FIG. 22 is a schematic cross section illustrating a step in thefabrication of an interferometric modulator in which a rivet structureis directly secured to an underlying optical stack.

FIGS. 23A-23E are schematic cross sections illustrating certain steps inthe fabrication of an interferometric modulator in which plating is usedto form an inorganic post.

FIGS. 24A-24B are schematic cross sections illustrating certain steps inthe fabrication of an interferometric modulator having support postsformed from an anodized material.

FIGS. 25A-25H are schematic cross-sections illustrating a method forfabricating an interferometric modulator element comprising supportstructures located above a movable layer and an additional supportstructure comprising sacrificial material located underneath the movablelayer.

FIGS. 26A-26B and 26D-26E are schematic cross sections illustratingcertain steps in the fabrication of an interferometric modulator havingan alternate support structure made from spin-on material. FIG. 26C is atop view of the partially fabricated interferometric modulator of FIG.26B.

FIG. 27 is a schematic cross-section illustrating an interferometricmodulator in which a portion of a support structure underlies a movablelayer, wherein the underlying portion of the support structure is formedat the same time as the overlying portion of the support supportstructure.

FIGS. 28A-28B are schematic cross sections illustrating certain steps inthe fabrication of an interferometric modulator in which plating is usedto form a rivet structure.

FIG. 29 is a top view illustrating a portion of an array ofinterferometric modulators and certain external components connected tothe strip electrodes within the array.

FIGS. 30A-30B are schematic cross sections illustrating certain steps inthe forming of a lead connected to a strip electrode, viewed along theline 30-30 of FIG. 29.

FIGS. 31A-31D are schematic cross sections illustrating certain steps inthe forming and passivating of a lead connected to a strip electrode,viewed along the line 31-31 of FIG. 29.

FIG. 32 is a schematic cross section illustrating a stage in analternate method of forming and passivating a lead connected to a stripelectrode, viewed along the line 31-31 of FIG. 29.

FIGS. 33A-33B are schematic cross-sections illustrating steps in amethod for fabricating an interferometric modulator having a movablelayer with varying stiffness due to residual patches of supportmaterial.

FIG. 34 illustrates a top view of an interferometric modulator elementformed using the steps of FIGS. 33A-33B.

FIGS. 35A-35H are schematic cross-sections illustrating steps in amethod for fabricating an interferometric modulator having a movablelayer which includes a reflective layer which is partially separatedfrom a mechanical layer and having a post structure which underlies atleast a portion of the movable layer.

FIGS. 36A-36C are schematic cross-sections illustrating steps in amethod for fabricating an interferometric modulator having stiffeningstructures formed on an upper surface of a reflective layer which ispartially separated from a mechanical layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following detailed description is directed to certain specificembodiments of the invention. However, the invention can be embodied ina multitude of different ways. In this description, reference is made tothe drawings wherein like parts are designated with like numeralsthroughout. As will be apparent from the following description, theembodiments may be implemented in any device that is configured todisplay an image, whether in motion (e.g., video) or stationary (e.g.,still image), and whether textual or pictorial. More particularly, it iscontemplated that the embodiments may be implemented in or associatedwith a variety of electronic devices such as, but not limited to, mobiletelephones, wireless devices, personal data assistants (PDAs), hand-heldor portable computers, GPS receivers/navigators, cameras, MP3 players,camcorders, game consoles, wrist watches, clocks, calculators,television monitors, flat panel displays, computer monitors, autodisplays (e.g., odometer display, etc.), cockpit controls and/ordisplays, display of camera views (e.g., display of a rear view camerain a vehicle), electronic photographs, electronic billboards or signs,projectors, architectural structures, packaging, and aestheticstructures (e.g., display of images on a piece of jewelry). MEMS devicesof similar structure to those described herein can also be used innon-display applications such as in electronic switching devices.

Individual MEMS elements, such as interferometric modulator elements,may be provided with support structures both within and at the edges ofindividual elements. In certain embodiments, these support structuresmay include support layers located over depressions in a movable layer.By forming these structures from rigid material such as aluminum oroxides, stability of the operation of the MEMS device can be improved ascompared with structures formed from less rigid material. In addition,the use of rigid material alleviates problems with gradual degradationor deformation of the support structures over time, which can lead to agradual shift in the color reflected by a given pixel. In addition,because these support structures overlie the MEMS device, they can bemade as thick as necessary without interfering with the operation of theMEMS device. In certain embodiments, overlying support structures mayextend through a movable layer to contact underlying fixed layers,anchoring and/or propping edge portions of the overlying supportstructure to the underlying layers. In other embodiments, residualpatches of support material may be used to stiffen portions of themovable layer, or to passivate exposed leads within or around the MEMSdevice.

One interferometric modulator display embodiment comprising aninterferometric MEMS display element is illustrated in FIG. 1. In thesedevices, the pixels are in either a bright or dark state. In the bright(“on” or “open”) state, the display element reflects a large portion ofincident visible light to a user. When in the dark (“off” or “closed”)state, the display element reflects little incident visible light to theuser. Depending on the embodiment, the light reflectance properties ofthe “on” and “off” states may be reversed. MEMS pixels can be configuredto reflect predominantly at selected colors, allowing for a colordisplay in addition to black and white.

FIG. 1 is an isometric view depicting two adjacent pixels in a series ofpixels of a visual display, wherein each pixel comprises a MEMSinterferometric modulator. In some embodiments, an interferometricmodulator display comprises a row/column array of these interferometricmodulators. Each interferometric modulator includes a pair of reflectivelayers positioned at a variable and controllable distance from eachother to form a resonant optical cavity with at least one variabledimension. In one embodiment, one of the reflective layers may be movedbetween two positions. In the first position, referred to herein as therelaxed position, the movable reflective layer is positioned at arelatively large distance from a fixed partially reflective layer. Inthe second position, referred to herein as the actuated position, themovable reflective layer is positioned more closely adjacent to thepartially reflective layer. Incident light that reflects from the twolayers interferes constructively or destructively depending on theposition of the movable reflective layer, producing either an overallreflective or non-reflective state for each pixel.

The depicted portion of the pixel array in FIG. 1 includes two adjacentinterferometric modulators 12 a and 12 b. In the interferometricmodulator 12 a on the left, a movable reflective layer 14 a isillustrated in a relaxed position at a predetermined distance from anoptical stack 16 a, which includes a partially reflective layer. In theinterferometric modulator 12 b on the right, the movable reflectivelayer 14 b is illustrated in an actuated position adjacent to theoptical stack 16 b.

The optical stacks 16 a and 16 b (collectively referred to as opticalstack 16), as referenced herein, typically comprise several fusedlayers, which can include an electrode layer, such as indium tin oxide(ITO), a partially reflective layer, such as chromium, and a transparentdielectric. The optical stack 16 is thus electrically conductive,partially transparent, and partially reflective, and may be fabricated,for example, by depositing one or more of the above layers onto atransparent substrate 20. The partially reflective layer can be formedfrom a variety of materials that are partially reflective such asvarious metals, semiconductors, and dielectrics. The partiallyreflective layer can be formed of one or more layers of materials, andeach of the layers can be formed of a single material or a combinationof materials.

In some embodiments, the layers of the optical stack 16 are patternedinto parallel strips, and may form row electrodes in a display device asdescribed further below. The movable reflective layers 14 a, 14 b may beformed as a series of parallel strips of a deposited metal layer orlayers (orthogonal to the row electrodes of 16 a, 16 b) deposited on topof posts 18 and an intervening sacrificial material deposited betweenthe posts 18. When the sacrificial material is etched away, the movablereflective layers 14 a, 14 b are separated from the optical stacks 16 a,16 b by a defined gap 19. A highly conductive and reflective materialsuch as aluminum may be used for the reflective layers 14, and thesestrips may form column electrodes in a display device.

With no applied voltage, the cavity 19 remains between the movablereflective layer 14 a and optical stack 16 a, with the movablereflective layer 14 a in a mechanically relaxed state, as illustrated bythe pixel 12 a in FIG. 1. However, when a potential difference isapplied to a selected row and column, the capacitor formed at theintersection of the row and column electrodes at the corresponding pixelbecomes charged, and electrostatic forces pull the electrodes together.If the voltage is high enough, the movable reflective layer 14 isdeformed and is forced against the optical stack 16. A dielectric layer(not illustrated in this Figure) within the optical stack 16 may preventshorting and control the separation distance between layers 14 and 16,as illustrated by pixel 12 b on the right in FIG. 1. The behavior is thesame regardless of the polarity of the applied potential difference. Inthis way, row/column actuation that can control the reflective vs.non-reflective pixel states is analogous in many ways to that used inconventional LCD and other display technologies.

FIGS. 2 through 5B illustrate one exemplary process and system for usingan array of interferometric modulators in a display application.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device that may incorporate aspects of the invention. In theexemplary embodiment, the electronic device includes a processor 21which may be any general purpose single-or multi-chip microprocessorsuch as an ARM, Pentium®, Pentium II®, Pentium III®, Pentium IV®,Pentium® Pro, an 8051, a MIPS®, a Power PC®, an ALPHA®, or any specialpurpose microprocessor such as a digital signal processor,microcontroller, or a programmable gate array. As is conventional in theart, the processor 21 may be configured to execute one or more softwaremodules. In addition to executing an operating system, the processor maybe configured to execute one or more software applications, including aweb browser, a telephone application, an email program, or any othersoftware application.

In one embodiment, the processor 21 is also configured to communicatewith an array driver 22. In one embodiment, the array driver 22 includesa row driver circuit 24 and a column driver circuit 26 that providesignals to a display array or panel 30. The cross section of the arrayillustrated in FIG. 1 is shown by the lines 1-1 in FIG. 2. For MEMSinterferometric modulators, the row/column actuation protocol may takeadvantage of a hysteresis property of these devices illustrated in FIG.3. It may require, for example, a 10 volt potential difference to causea movable layer to deform from the relaxed state to the actuated state.However, when the voltage is reduced from that value, the movable layermaintains its state as the voltage drops back below 10 volts. In theexemplary embodiment of FIG. 3, the movable layer does not relaxcompletely until the voltage drops below 2 volts. Thus, there exists awindow of applied voltage, about 3 to 7 V in the example illustrated inFIG. 3, within which the device is stable in either the relaxed oractuated state. This is referred to herein as the “hysteresis window” or“stability window.” For a display array having the hysteresischaracteristics of FIG. 3, the row/column actuation protocol can bedesigned such that during row strobing, pixels in the strobed row thatare to be actuated are exposed to a voltage difference of about 10volts, and pixels that are to be relaxed are exposed to a voltagedifference of close to zero volts. After the strobe, the pixels areexposed to a steady state voltage difference of about 5 volts such thatthey remain in whatever state the row strobe put them in. After beingwritten, each pixel sees a potential difference within the “stabilitywindow” of 3-7 volts in this example. This feature makes the pixeldesign illustrated in FIG. 1 stable under the same applied voltageconditions in either an actuated or relaxed pre-existing state. Sinceeach pixel of the interferometric modulator, whether in the actuated orrelaxed state, is essentially a capacitor formed by the fixed and movingreflective layers, this stable state can be held at a voltage within thehysteresis window with almost no power dissipation. Essentially nocurrent flows into the pixel if the applied potential is fixed.

In typical applications, a display frame may be created by asserting theset of column electrodes in accordance with the desired set of actuatedpixels in the first row. A row pulse is then applied to the row 1electrode, actuating the pixels corresponding to the asserted columnlines. The asserted set of column electrodes is then changed tocorrespond to the desired set of actuated pixels in the second row. Apulse is then applied to the row 2 electrode, actuating the appropriatepixels in row 2 in accordance with the asserted column electrodes. Therow 1 pixels are unaffected by the row 2 pulse, and remain in the statethey were set to during the row 1 pulse. This may be repeated for theentire series of rows in a sequential fashion to produce the frame.Generally, the frames are refreshed and/or updated with new display databy continually repeating this process at some desired number of framesper second. A wide variety of protocols for driving row and columnelectrodes of pixel arrays to produce display frames are also well knownand may be used in conjunction with the present invention.

FIGS. 4, 5A, and 5B illustrate one possible actuation protocol forcreating a display frame on the 3×3 array of FIG. 2. FIG. 4 illustratesa possible set of column and row voltage levels that may be used forpixels exhibiting the hysteresis curves of FIG. 3. In the FIG. 4embodiment actuating a pixel involves setting the appropriate column to−V_(bias), and the appropriate row to +ΔV, which may correspond to −5volts and +5 volts, respectively Relaxing the pixel is accomplished bysetting the appropriate column to +V_(bias), and the appropriate row tothe same +ΔV, producing a zero volt potential difference across thepixel. In those rows where the row voltage is held at zero volts, thepixels are stable in whatever state they were originally in, regardlessof whether the column is at +V_(bias), or −V_(bias). As is alsoillustrated in FIG. 4, it will be appreciated that voltages of oppositepolarity than those described above can be used, e.g., actuating a pixelcan involve setting the appropriate column to +V_(bias), and theappropriate row to −ΔV. In this embodiment, releasing the pixel isaccomplished by setting the appropriate column to −V_(bias), and theappropriate row to the same −ΔV, producing a zero volt potentialdifference across the pixel.

FIG. 5B is a timing diagram showing a series of row and column signalsapplied to the 3×3 array of FIG. 2 which will result in the displayarrangement illustrated in FIG. 5A, where actuated pixels arenon-reflective. Prior to writing the frame illustrated in FIG. 5A, thepixels can be in any state, and in this example, all the rows are at 0volts, and all the columns are at +5 volts. With these applied voltages,all pixels are stable in their existing actuated or relaxed states.

In the FIG. 5A frame, pixels (1,1), (1,2), (2,2), (3,2) and (3,3) areactuated. To accomplish this, during a “line time” for row 1, columns 1and 2 are set to −5 volts, and column 3 is set to +5 volts. This doesnot change the state of any pixels, because all the pixels remain in the3-7 volt stability window. Row 1 is then strobed with a pulse that goesfrom 0, up to 5 volts, and back to zero. This actuates the (1,1) and(1,2) pixels and relaxes the (1,3) pixel. No other pixels in the arrayare affected. To set row 2 as desired, column 2 is set to −5 volts, andcolumns 1 and 3 are set to +5 volts. The same strobe applied to row 2will then actuate pixel (2,2) and relax pixels (2,1) and (2,3). Again,no other pixels of the array are affected. Row 3 is similarly set bysetting columns 2 and 3 to −5 volts, and column 1 to +5 volts. The row 3strobe sets the row 3 pixels as shown in FIG. 5A. After writing theframe, the row potentials are zero, and the column potentials can remainat either +5 or −5 volts, and the display is then stable in thearrangement of FIG. 5A. It will be appreciated that the same procedurecan be employed for arrays of dozens or hundreds of rows and columns. Itwill also be appreciated that the timing, sequence, and levels ofvoltages used to perform row and column actuation can be varied widelywithin the general principles outlined above, and the above example isexemplary only, and any actuation voltage method can be used with thesystems and methods described herein.

FIGS. 6A and 6B are system block diagrams illustrating an embodiment ofa display device 40. The display device 40 can be, for example, acellular or mobile telephone. However, the same components of displaydevice 40 or slight variations thereof are also illustrative of varioustypes of display devices such as televisions and portable media players.

The display device 40 includes a housing 41, a display 30, an antenna43, a speaker 45, an input device 48, and a microphone 46. The housing41 is generally formed from any of a variety of manufacturing processesas are well known to those of skill in the art, including injectionmolding and vacuum forming. In addition, the housing 41 may be made fromany of a variety of materials, including, but not limited to, plastic,metal, glass, rubber, and ceramic, or a combination thereof. In oneembodiment, the housing 41 includes removable portions (not shown) thatmay be interchanged with other removable portions of different color, orcontaining different logos, pictures, or symbols.

The display 30 of the exemplary display device 40 may be any of avariety of displays, including a bi-stable display, as described herein.In other embodiments, the display 30 includes a flat-panel display, suchas plasma, EL, OLED, STN LCD, or TFT LCD as described above, or anon-flat-panel display, such as a CRT or other tube device, as is wellknown to those of skill in the art. However, for purposes of describingthe present embodiment, the display 30 includes an interferometricmodulator display, as described herein.

The components of one embodiment of the exemplary display device 40 areschematically illustrated in FIG. 6B. The illustrated exemplary displaydevice 40 includes a housing 41 and can include additional components atleast partially enclosed therein. For example, in one embodiment, theexemplary display device 40 includes a network interface 27 thatincludes an antenna 43, which is coupled to a transceiver 47. Thetransceiver 47 is connected to a processor 21, which is connected toconditioning hardware 52. The conditioning hardware 52 may be configuredto condition a signal (e.g., filter a signal). The conditioning hardware52 is connected to a speaker 45 and a microphone 46. The processor 21 isalso connected to an input device 48 and a driver controller 29. Thedriver controller 29 is coupled to a frame buffer 28 and to an arraydriver 22, which in turn is coupled to a display array 30. A powersupply 50 provides power to all components as required by the particularexemplary display device 40 design.

The network interface 27 includes the antenna 43 and the transceiver 47so that the exemplary display device 40 can communicate with one or moredevices over a network. In one embodiment, the network interface 27 mayalso have some processing capabilities to relieve requirements of theprocessor 21. The antenna 43 is any antenna known to those of skill inthe art for transmitting and receiving signals. In one embodiment, theantenna transmits and receives RF signals according to the IEEE 802.11standard, including IEEE 802.11(a), (b), or (g). In another embodiment,the antenna transmits and receives RF signals according to the BLUETOOTHstandard. In the case of a cellular telephone, the antenna is designedto receive CDMA, GSM, AMPS, or other known signals that are used tocommunicate within a wireless cell phone network. The transceiver 47pre-processes the signals received from the antenna 43 so that they maybe received by and further manipulated by the processor 21. Thetransceiver 47 also processes signals received from the processor 21 sothat they may be transmitted from the exemplary display device 40 viathe antenna 43.

In an alternative embodiment, the transceiver 47 can be replaced by areceiver. In yet another alternative embodiment, the network interface27 can be replaced by an image source, which can store or generate imagedata to be sent to the processor 21. For example, the image source canbe memory device such as a digital video disc (DVD) or a hard-disc drivethat contains image data, or a software module that generates imagedata.

The processor 21 generally controls the overall operation of theexemplary display device 40. The processor 21 receives data, such ascompressed image data from the network interface 27 or an image source,and processes the data into raw image data or into a format that isreadily processed into raw image data. The processor 21 then sends theprocessed data to the driver controller 29 or to the frame buffer 28 forstorage. Raw data typically refers to the information that identifiesthe image characteristics at each location within an image. For example,such image characteristics can include color, saturation, and gray-scalelevel.

In one embodiment, the processor 21 includes a microcontroller, CPU, orlogic unit to control operation of the exemplary display device 40. Theconditioning hardware 52 generally includes amplifiers and filters fortransmitting signals to the speaker 45, and for receiving signals fromthe microphone 46. The conditioning hardware 52 may be discretecomponents within the exemplary display device 40, or may beincorporated within the processor 21 or other components.

The driver controller 29 takes the raw image data generated by theprocessor 21 either directly from the processor 21 or from the framebuffer 28 and reformats the raw image data appropriately for high speedtransmission to the array driver 22. Specifically, the driver controller29 reformats the raw image data into a data flow having a raster-likeformat, such that it has a time order suitable for scanning across thedisplay array 30. Then the driver controller 29 sends the formattedinformation to the array driver 22. Although a driver controller 29,such as a LCD controller, is often associated with the system processor21 as a stand-alone Integrated Circuit (IC), such controllers may beimplemented in many ways. They may be embedded in the processor 21 ashardware, embedded in the processor 21 as software, or fully integratedin hardware with the array driver 22.

Typically, the array driver 22 receives the formatted information fromthe driver controller 29 and reformats the video data into a parallelset of waveforms that are applied many times per second to the hundredsand sometimes thousands of leads coming from the display's x-y matrix ofpixels.

In one embodiment, the driver controller 29, the array driver 22, andthe display array 30 are appropriate for any of the types of displaysdescribed herein. For example, in one embodiment, the driver controller29 is a conventional display controller or a bi-stable displaycontroller (e.g., an interferometric modulator controller). In anotherembodiment, the array driver 22 is a conventional driver or a bi-stabledisplay driver (e.g., an interferometric modulator display). In oneembodiment, a driver controller 29 is integrated with the array driver22. Such an embodiment is common in highly integrated systems such ascellular phones, watches, and other small area displays. In yet anotherembodiment, the display array 30 is a typical display array or abi-stable display array (e.g., a display including an array ofinterferometric modulators).

The input device 48 allows a user to control the operation of theexemplary display device 40. In one embodiment, the input device 48includes a keypad, such as a QWERTY keyboard or a telephone keypad, abutton, a switch, a touch-sensitive screen, or a pressure-orheat-sensitive membrane. In one embodiment, the microphone 46 is aninput device for the exemplary display device 40. When the microphone 46is used to input data to the device, voice commands may be provided by auser for controlling operations of the exemplary display device 40.

The power supply 50 can include a variety of energy storage devices asare well known in the art. For example, in one embodiment, the powersupply 50 is a rechargeable battery, such as a nickel-cadmium battery ora lithium ion battery. In another embodiment, the power supply 50 is arenewable energy source, a capacitor, or a solar cell including aplastic solar cell, and solar-cell paint. In another embodiment, thepower supply 50 is configured to receive power from a wall outlet.

In some embodiments, control programmability resides, as describedabove, in a driver controller which can be located in several places inthe electronic display system. In some embodiments, controlprogrammability resides in the array driver 22. Those of skill in theart will recognize that the above-described optimizations may beimplemented in any number of hardware and/or software components and invarious configurations.

The details of the structure of interferometric modulators that operatein accordance with the principles set forth above may vary widely. Forexample, FIGS. 7A-7E illustrate five different embodiments of themovable reflective layer 14 and its supporting structures. FIG. 7A is across section of the embodiment of FIG. 1, where a strip of metalmaterial 14 is deposited on orthogonally extending supports 18. In FIG.7B, the moveable reflective layer 14 is attached to supports 18 at thecorners only, on tethers 32. In FIG. 7C, the moveable reflective layer14 is suspended from a deformable layer 34, which may comprise aflexible metal. The deformable layer 34 connects, directly orindirectly, to the substrate 20 around the perimeter of the deformablelayer 34. These connections are herein referred to as supportstructures, which can take the form of isolated pillars or posts and/orcontinuous walls or rails. The embodiment illustrated in FIG. 7D hassupport structures 18 that include support plugs 42 upon which thedeformable layer 34 rests. The movable reflective layer 14 remainssuspended over the cavity, as in FIGS. 7A-7C, but the deformable layer34 does not form the support posts by filling holes between thedeformable layer 34 and the optical stack 16. Rather, the support posts18 are formed of a planarization material, which is used to form thesupport post plugs 42. The embodiment illustrated in FIG. 7E is based onthe embodiment shown in FIG. 7D, but may also be adapted to work withany of the embodiments illustrated in FIGS. 7A-7C, as well as additionalembodiments not shown. In the embodiment shown in FIG. 7E, an extralayer of metal or other conductive material has been used to form a busstructure 44. This allows signal routing along the back of theinterferometric modulators, eliminating a number of electrodes that mayotherwise have had to be formed on the substrate 20.

In embodiments such as those shown in FIG. 7, the interferometricmodulators function as direct-view devices, in which images are viewedfrom the front side of the transparent substrate 20, the side oppositeto that upon which the modulator is arranged. In these embodiments, thereflective layer 14 optically shields the portions of theinterferometric modulator on the side of the reflective layer oppositethe substrate 20, including the deformable layer 34. This allows theshielded areas to be configured and operated upon without negativelyaffecting the image quality. Such shielding allows the bus structure 44in FIG. 7E, which provides the ability to separate the opticalproperties of the modulator from the electromechanical properties of themodulator, such as addressing and the movements that result from thataddressing. This separable modulator architecture allows the structuraldesign and materials used for the electromechanical aspects and theoptical aspects of the modulator to be selected and to functionindependently of each other. Moreover, the embodiments shown in FIGS.7C-7E have additional benefits deriving from the decoupling of theoptical properties of the reflective layer 14 from its mechanicalproperties, which are carried out by the deformable layer 34. Thisallows the structural design and materials used for the reflective layer14 to be optimized with respect to the optical properties, and thestructural design and materials used for the deformable layer 34 to beoptimized with respect to desired mechanical properties.

In certain embodiments, it may be desirable to provide additionalsupport to a movable layer such as the movable reflective layer 14illustrated in FIG. 7A, or the combination of mechanical layer 34 andmovable reflective layer 14 of FIGS. 7C-7E. The movable layer maycomprise a reflective sublayer and a mechanical sublayer, as will bediscussed in greater detail below. Such support may be provided by aseries of support structures which may be located both along the edgesof an individual modulator element and in the interior of such anelement. In various embodiments, these support structures may be locatedeither over or underneath a movable layer. In alternate embodiments,support structures may extend through an aperture formed in themechanical layer, such that support is provided from both above andbelow the mechanical layer. As used herein, the term “rivet” generallyrefers to a patterned layer overlying a mechanical layer in a MEMSdevice, usually in a recess or depression in the post or support region,to lend mechanical support for the mechanical layer. Preferably, thoughnot always, the rivet includes wings overlying an upper surface of themechanical layer to add stability and predictability to the mechanicallayer's movement. Similarly, support structures underlying a mechanicallayer in a MEMS device to lend mechanical support for the mechanicallayer are generally referred to herein as support “posts.” In many ofthe embodiments herein, the preferred materials are inorganic forstability relative to organic resist materials.

An exemplary layout of such support structures is shown in FIG. 8, whichdepicts an array of MEMS elements. In certain embodiments, the array maycomprise an array of interferometric modulators, but in alternateembodiments, the MEMS elements may comprise any MEMS device having amovable layer. It can be seen that support structures 62, which in theillustrated embodiment are overlying rivet structures 62, are locatedboth along the edges of a movable layer 66 and in the interior of a MEMSelement, in this example an interferometric modulator element 60.Certain support structures may comprise rail structures 64, which extendacross the gap 65 between two adjacent movable layers 66. It can be seenthat movable layer 66 comprises a strip of deformable material extendingthrough multiple adjacent elements 60 within the same column. Thesupport structures 62 serve to stiffen the movable layer 66 within theelements or pixels 60.

Advantageously, these support structures 62 are made small relative tothe surrounding area of the modulator element 60. As the support postsconstrain deflection of the movable layer 66 and may generally beopaque, the area underneath and immediately surrounding the supportstructures 62 is not usable as active area in a display, as the movablelayer in those areas is not movable to a fully actuated position (e.g.,one in which a portion of the lower surface of the movable layer 14 ofFIG. 7A is in contact with the upper surface of the optical stack 16).Because this may result in undesirable optical effects in the areassurrounding the post, a mask layer may advantageously be providedbetween the support structures and the viewer to avoid excessivereflection in these regions that may wash out the intended color.

In certain embodiments, these support structures may comprise adepression in the movable layer, along with a substantially rigidstructure which helps to maintain the shape. While such supportstructures may be formed of a polymer material, an inorganic materialhaving greater rigidity is preferably used, and provides advantages oversimilar structures comprising polymeric materials.

For instance, a polymeric support structure may not maintain a desiredlevel of rigidity over a wide range of operating temperatures, and maybe subject to gradual deformation or mechanical failure over thelifetime of a device. As such failures may affect the distance betweenthe movable layer and the optical stack, and this distance at leastpartially determines the wavelengths reflected by the interferometricmodulator element, such failures may lead to a shift in the reflectedcolor due to wear over time or variance in operating temperatures. OtherMEMS devices experience analogous degradation over time when supportsare formed of polymeric material.

One process for forming an interferometric modulator element comprisingoverlying rivet support structures is described with respect to FIGS.9A-9J. In FIG. 9A, it can be seen that a transparent substrate 70 isprovided, which may comprise, for example, glass or a transparentpolymeric material. A conductive layer 72, which may compriseindium-tin-oxide (ITO) is then deposited over the transparent substrate,and a partially reflective layer 74, which may comprise chromium, isdeposited over the conductive layer 72. Although in one embodimentconductive layer 72 may comprise ITO, and may be referred to as such atvarious points in the below specification, it will be understood thatthe layer 72 may comprise any suitable conductive material, and need notbe transparent for non-optical MEMS structures. Similarly, althoughsometimes referred to as a chromium layer, partially reflective layer 74may comprise any suitable partially reflective layer, and may be omittedfor non-optical MEMS structures.

The conductive layer 72 and partially reflective layer 74 are thenpatterned and etched to form bottom electrodes, also referred to as rowelectrodes, which run perpendicular to the movable layer 66 of FIG. 8.In certain embodiments, the conductive and partially reflective layers72 and 74 may advantageously also be patterned and etched to remove theITO and chromium underlying the areas where the support post structureswill be located, forming apertures 76 as depicted in FIG. 9B. Thispatterning and etching is preferably done by the same process whichforms the row electrodes. The removal of ITO and chromium (or otherconductive materials) underlying the support structures helps to preventshorting between the movable layer and the bottom electrode. Thus, FIG.9B and the subsequent figures depict a cross-section of a continuous rowelectrode formed by layers 72 and 74, in which apertures 76 have beenetched, taken along a line extending through those apertures. In otherembodiments in which the conductive layer 72 and partially reflectivelayer 74 are not etched to form apertures 76, a dielectric layer,discussed below, may provide sufficient protection against shortingbetween the bottom electrode and the movable layer.

The conductive layer 72 and partially reflective layer 74 may bepatterned via photolithography and etched via, for example, commerciallyavailable wet etches. Chromium wet etches include solutions of AceticAcid (C₂H₄O₂) and Cerium Ammonium Nitrate [Ce(NH₄)₂(NO₃)₆]. ITO wetetches include HCl, a mixture of HCl and HNO₃, or a mixture ofFeCl₃/HCl/DI in a 75%/3%/22% ratio and H₂O. Once the apertures 76 havebeen formed, a dielectric layer 78 is deposited over the conductive andpartially reflective layers 72 and 74, as seen in FIG. 9C, forming theoptical stack 16. In certain embodiments, the dielectric layer maycomprise SiO₂ or SiN_(x), although a wide variety of suitable materialsmay be used.

The thickness and positioning of the layers forming the optical stack 16determines the color reflected by the interferometric modulator elementwhen the element is actuated (collapsed), bringing the movable layer 66into contact with the optical stack. In certain embodiments, the opticalstack is configured such that the interferometric modulator elementreflects substantially no visible light (appears black) when the movablelayer is in an actuated position. Typically, the thickness of thedielectric layer 78 is about 450 Å. While illustrated as planar (whichcan be achieved if the dielectric layer 78 is a spin-on glass), thedielectric layer 78 is typically conformal over the patterned lowerelectrode formed from layers 72 and 74.

As seen in FIG. 9D, a layer 82 of sacrificial material is then depositedover the dielectric layer 78. In certain embodiments, this sacrificiallayer 82 is formed from a material which is etchable by XeF₂. Forexample, the sacrificial layer 82 may be formed from molybdenum oramorphous silicon (a—Si). In other embodiments, the sacrificial layermay comprise tantalum or tungsten. Other materials which are usable assacrificial materials include silicon nitride, certain oxides, andorganic materials. The thickness of the deposited sacrificial layer 82will determine the distance between the optical stack 16 and the movablelayer 66, thus defining the dimensions of the interferometric gap 19(see FIG. 7A). As the height of the gap 19 determines the colorreflected by the interferometric modulator element when in an unactuatedposition, the thickness of the sacrificial layer 82 will vary dependingon the desired characteristics of the interferometric modulator. Forinstance, in an embodiment in which a modulator element that reflectsgreen in the unactuated position is formed, the thickness of thesacrificial layer 82 may be roughly 2000 Å. In further embodiments, thesacrificial layer may have multiple thicknesses across an array of MEMSdevices, such as in a multicolor display system where differentinterferometric gap sizes are used to produce different colors.

In FIG. 9E, it can be seen that the sacrificial layer 82 has beenpatterned and etched to form tapered apertures 86. The apertures 86overlie the apertures 76 cut into the layers 72 and 74 of ITO andchromium. These apertures 86 may be formed by masking the sacrificiallayer, using photolithography, and then performing either a wet or dryetch to remove portions of the sacrificial material. Suitable dry etchesinclude, but are not limited to, SF₆, CF₄, Cl₂, or any mixture of thesegases with O₂ or a noble gas such as He or Ar. Wet etches suitable foretching Mo include a PAN etch, which may be a mix of phosphoric acid,acetic acid, nitric acid and deionized water in a 16:1:1:2 ratio.Amorphous silicon can be etched by wet etches including KOH and HFNitrate. Preferably, however a dry etch is used to etch the sacrificiallayer 82, as dry etches permit more control over the shape of taperedapertures 86.

In FIG. 9F, it can be seen that the components which will form themovable layer 66 (see, e.g., moveable reflective layer 14 in FIG. 7A)are then deposited over the etched sacrificial layer 82, lining thetapered apertures 86. In the embodiment of FIG. 9F, a highly reflectivelayer 90, also referred to as a mirror or mirror layer, is depositedfirst, followed by a mechanical layer 92. The highly reflective layer 90may be formed from aluminum or an aluminum alloy, due to their highreflectance over a wide spectrum of wavelengths. The mechanical layer 92may comprise a metal such as Ni and Cr, and is preferably formed suchthat the mechanical layer 92 contains residual tensile stress. Theresidual tensile stress provides the mechanical force which pulls themovable layer 66 away from the optical stack 16 when the modulator isunactuated, or “relaxed.” For convenience, the combination of the highlyreflective layer 90 and mechanical layer 92 may be collectively referredto as movable layer 66, although it will be understood that the termmovable layer, as used herein, also encompasses a partially separatedmechanical and reflective layer, such as the mechanical layer 34 and themovable reflective layer 14 of FIG. 7C, the fabrication of which inconduction with support structures is discussed below with respect toFIGS. 35A-35H and 36A-36C.

In an embodiment in which the sacrificial layer is to be etched by aXeF₂ etch, both the reflective layer 90 and the mechanical layer 92 arepreferably resistant to XeF₂ etching. If either of these layers is notresistant an etch stop layer may be used to protect the non-resistantlayer. It can also be seen that the taper of the tapered apertures 86facilitates the conformal deposition of the reflective layer 90 andmechanical layer 92, as they may comprise non-planarizing materials.Absent this taper, it may be difficult to deposit these layers such thatthe layers have substantially even thicknesses within the apertures 86.

In an alternate embodiment, the movable layer 66 may comprise a singlelayer which is both highly reflective and has the desired mechanicalcharacteristics. However, the deposition of two distinct layers permitsthe selection of a highly reflective material, which might otherwise beunsuitable if used as the sole material in a movable layer 66, andsimilarly allows selection of a suitable mechanical layer without regardto its reflective properties. In yet further embodiments, the movablelayer may comprise a reflective sublayer which is largely detached fromthe mechanical layer, such that the reflective layer may be translatedvertically without bending (See, e.g., FIGS. 7C-7E and attendantdescription). One method of forming such an embodiment comprises thedeposition of a reflective layer over the sacrificial layer, which isthen patterned to form individual reflective sublayers. A second layerof sacrificial material is then deposited over the reflective layer andpatterned to permit the connections to be made through the secondsacrificial layer between the mechanical sublayer and the reflectivesublayers, as well as to form tapered apertures for the supportstructures.

In other embodiments in which the MEMS devices being formed comprisenon-optical MEMS devices (e.g., a MEMS switch), it will be understoodthat the movable layer 66 need not comprise a reflective material. Forinstance, in embodiments in which MEMS devices such as MEMS switches arebeing formed comprising the support structures discussed herein, theunderside of the movable layer 66 need not be reflective, and mayadvantageously comprise a single layer, selected solely on the basis ofits mechanical properties or other desirable properties.

In FIG. 9G, a rigid layer 96, also referred to as a rivet layer, isdeposited over the mechanical layer 92. As the rivet layer 96 will forma structure which provides support to the underlying mechanical layer 92but will not be substantially deformed during actuation of themodulator, the material forming the rivet layer 96 need not be asflexible as that forming the mechanical layer 92. Suitable materials foruse in the rivet layer 96 include, but are not limited to, aluminum,AlO_(x), silicon oxide, SiN_(x), nickel and chromium. Alternatematerials which may be used to form the rivet structure include othermetals, ceramics, and polymers. The thickness of the rivet layer 96 willvary according to the mechanical properties of the material used.

As discussed with respect to the mechanical and reflective layers, itmay be desirable to select for the rivet layer 96 a material that isresistant to XeF₂ etching, which may be used to etch the sacrificiallayer in certain embodiments. In addition, the rivet layer 96 ispreferably selectively etchable with respect to the underlyingmechanical layer 92, so as to permit etching of the rivet layer 96 whileleaving the mechanical layer 92 unaffected. However, if the rivet layer96 is not selectively etchable relative to the mechanical layer 92, anetch stop layer (not shown) may be provided between the rivet layer 96and the mechanical layer 92.

In FIG. 9H, the rivet layer 96 is patterned via photolithography andetched to remove portions of the rivet layer 96 located away from theapertures 86, forming support structures 62, also referred to as rivetstructures. The etching of the rivet layer 96 may be performed by eithera wet etch or a dry etch. In embodiments in which the rivet layer 96comprises aluminum, suitable wet etches include phosphoric acid or basessuch as KOH, TMAH, and NaOH, and a suitable dry etch uses Cl₂. In otherembodiments in which the rivet layer 96 comprises SiO₂, a mixture offluorine-bases gases and either O₂ or noble gases may be used as a dryetch, and HF or BOE are suitable wet etches.

Referring still to FIG. 9H, it can be seen that the support structures62 may comprise a lip area 98, where the support structure 62 extendsout of the tapered aperture 86 over the upper surface of the mechanicallayer 92. Advantageously, the size of this lip can be minimized, as thelip constrains deflection of the underlying mechanical layer, reducingthe active area of the interferometric modulator element. As can be seenin the illustrated embodiment, the support structures 62 may alsocomprise a sloped sidewall portion 97 and a substantially flat base area99.

Next, in FIG. 9I, it can be seen that photolithography is used topattern the mechanical layer 92, and etch the mechanical layer 92 andthe reflective layer 90 to form etch holes 100, which expose portions ofthe sacrificial layer 82, in order to facilitate etching of thesacrificial layer. In certain embodiments, multiple etches are employedto expose the sacrificial layer. For example, if the mechanical layer 92comprises nickel and the reflective layer 90 comprises aluminum, HNO₃may be used to etch the mechanical layer 92, and phosphoric acid or abase such as NH₄OH, KOH, THAM, or NaOH may be used to etch thereflective layer 90. This patterning and etching may also be used todefine the strip electrodes seen in FIG. 8, by etching gaps 65 betweenstrips of the movable layer 66 (see FIG. 8), separating columns of MEMSdevices from one another.

Finally, in FIG. 9J, it can be seen that a release etch is performed toremove the sacrificial layer, creating the interferometric gap 19through which the movable layer 66 can move. In certain embodiments, aXeF₂ etch is used to remove the sacrificial layer 82. Because XeF₂etches the sacrificial materials well, and is extremely selectiverelative to other materials used in the processes discussed above, theuse of a XeF₂ etch advantageously permits the removal of the sacrificialmaterial with very little effect on the surrounding structures.

Thus, FIG. 9J depicts a portion of an interferometric modulator elementsuch as one of the interferometric modulator elements 60 of FIG. 8,shown along line 9J-9J. In this embodiment, the movable layer 66 issupported throughout the gap 19 by support structures 62 formed overdepressions 86 in the movable layer 66. As discussed above, portions ofthe underlying optical stack 16 have advantageously been etched so as toprevent shorting between conductive portions of the optical stack 16 andconductive layers in the movable layer 66, although this step need notbe performed in all embodiments.

Although the thickness of the rivet layer 96 deposited in FIG. 9G may bedetermined based upon the mechanical characteristics of the materialused, in alternate embodiments, the rivet layer 96 may be made muchthicker than merely sufficient for the function of providing support forthe mechanical layer. FIG. 10 depicts a portion of an interferometricmodulator in which the support structures 62 have been formed from amuch thicket rivet layer. Such an embodiment enables the supportstructures 62 to perform other functions, such as supporting additionalcomponents of the modulator (see FIG. 7E and attendant description),providing spacers to protect the interferometric modulator element fromdamage due to mechanical interference with the movable layer 66, or tosupport a protective backplate. In certain embodiments the thickness ofthe rivet layer may be between 300 Å and 1000 Å. In other embodiments,the thickness of the rivet layer may be between 1000 Å and 10 microns.In other embodiments, the thickness of the rivet layer may be 20 micronsor higher. In certain embodiments, the thickness of the rivet layer maybe between 0.1 and 0.6 times the thickness of the mechanical layer. Inother embodiments, the thickness of the rivet layer may be between 0.6and 1 times the thickness of the mechanical layer. In other embodiments,the thickness of the rivet layer may be between 1 and 200 times thethickness of the mechanical layer. It will be understood that in certainembodiments, thicknesses both within and outside of the above ranges maybe appropriate.

In an embodiment in which the movable layer 66 comprises a conductivereflective layer 90, the separate mechanical layer 92 can be omitted,and the rivet layer 96 may serve as the mechanical layer, while theconductive reflective layer 90 may provide the desired electricalconnectivity across a MEMS array, serving as the electrodes. In afurther embodiment, the conductive reflective layer 90 may be madethicker than is necessary to provide the desired optical characteristicsin order to provide better conductive characteristics, such as bylowering the resistivity of the strip electrodes formed from thepatterned conductive reflective layer 90.

In another variation, a thick mechanical layer may be deposited afterperforming the steps described with respect to FIGS. 9A-9E. This thickmechanical layer may subsequently be polished down or otherwise etchedback to achieve a desired thickness in those portions overlying theremaining sacrificial layer. However, as the mechanical layer isinitially thicker than the desired final thickness in the areasoverlying the sacrificial material, a thicker mechanical layer willremain in the apertures in the sacrificial layer, untouched by thepolishing, providing support similar to that resulting from the supportstructures 62 (see, e.g., FIG. 9H), as discussed above. Advantageously,the mechanical layer may be thick enough to totally fill the aperturesin the sacrificial layer, although it will be understood that sufficientsupport may be provided with a thinner mechanical layer in certainembodiments.

In another embodiment, the support structures may take the form ofinorganic posts underlying the movable layer. An exemplary process forfabricating an interferometric modulator comprising inorganic supportposts is discussed with respect to FIGS. 11A-11G, the early steps ofwhich process may correspond generally to the early steps in the processof FIGS. 9A-9J. In various embodiments, as discussed above, fabricatingan interferometric modulator comprises forming an optical stack on asubstrate, which may be a light-transmissive substrate, and in furtherembodiments is a transparent substrate. The optical stack may comprise aconductive layer, which forms an electrode layer on or adjacent thesubstrate; a partially reflective layer, which reflects some incidentlight while permitting some light to reach the other components of theinterferometric modulator element; and a dielectric layer, whichinsulates the underlying electrode layer from the other components ofthe interferometric modulator. In FIG. 11A, it can be seen that atransparent substrate 70 is provided, and that a conductive layer 72 anda partially reflective layer 74 are deposited over the substrate 70. Adielectric layer 78 is then deposited over the partially reflectivelayer 74.

As discussed above, in some embodiments, the conductive layer 72 istransparent and comprises ITO, the partially reflective layer 74comprises a semireflective thickness of metal, such as chromium (Cr),and the dielectric layer 78 comprises silicon oxide (SiO₂). At somepoint during this process, at least the conductive layer 72 is patterned(as shown in FIG. 9B) to form row electrodes which will be used toaddress a row of interferometric modulators. In one embodiment, thispatterning takes place after the deposition of the conductive andpartially reflective layers 72 and 74, but prior to the deposition ofthe dielectric layer 78. In a further embodiment, the conductive andpartially reflective layers 72 and 74 are patterned so as to form gaps(not shown) underneath the support structures, so as to minimize thepossibility of a short between the layers 72 and 74 and an overlyingconductive layer forming part of or extending underneath the supportstructure.

The combination of the layers 72, 74, and 78 is referred to herein asthe optical stack 16, and may be indicated by a single layer in laterfigures, for convenience. It will be understood that the composition ofthe optical stack 16 may vary both in the number of layers and thecomponents of those layers, and that the layers discussed above aremerely exemplary.

A variety of methods can be used to perform the patterning and etchingprocesses discussed with respect to the various embodiments disclosedherein. The etches used may be either a dry etch or a wet etch, and maybe isotropic or anisotropic. Suitable dry etches include, but are notlimited to: SF₆/O₂, CHF₃/O₂, SF₂/O₂, CF₄/O₂, and NF₃/O₂. Generally,these etches are suitable for etching one or more of SiO_(x), SiN_(x),SiO_(x)N_(y), spin-on glass, Nissan™ hard coat, and TaO_(x), but othermaterials may also be etched by this process. Materials which areresistant to one or more of these etches, and may thus be used as etchbarrier layers, include but are not limited to Al, Cr, Ni, and Al₂O₃. Inaddition, wet etches including but not limited to PAD etches, BHF, KOH,and phosphoric acid may be utilized in the processes described herein,and may generally be used to etch metallic materials. Generally, theseetches may be isotropic, but can be made anisotropic through the use ofa reactive ion etch (RIE), by ionizing the etch chemicals and shootingthe ions at the substrate. The patterning may comprise the deposition ofa photoresist (PR) layer (either positive or negative photoresist),which is then used to form a mask. Alternately, a hard mask can beutilized. In some embodiments, the hard mask may comprise metal orSiN_(x), but it will be understood that the composition of the hard maskmay depend on the underlying materials to be etched and the selectivityof the etch to be used. In The hard mask is typically patterned using aPR layer, which is then removed, and the hard mask is used as a mask toetch an underlying layer. The use of a hard mask may be particularlyadvantageous when a wet etch is being used, or whenever processingthrough a mask under conditions that a PR mask cannot handle (such as athigh temperatures, or when using an oxygen-based etch). Alternatemethods of removing layers may also be utilized, such as an ashing etchor lift-off processes.

In FIG. 11B, it can be seen that a layer 82 of sacrificial material isdeposited over the optical stack 16. In FIG. 11C, the sacrificial layer82 has been patterned and etched to form tapered apertures 86, whichcorrespond to the locations of post or support regions. These apertures86 are advantageously tapered in order to facilitate continuous andconformal deposition of overlying layers.

In FIG. 11D, a layer 84 of inorganic post material is deposited over thepatterned sacrificial layer 82, such that the inorganic post layer 84also coats the side walls and the base of the tapered apertures 86. Incertain embodiments, the inorganic post layer 84 is thinner than thesacrificial layer 82, and is conformal over the sacrificial layer 82. Inother embodiments, post layer 84 may have a thickness between 1000 Å and5000 Å. It will be understood that depending on the embodiment and thematerials being used, thicknesses both less than this range and greaterthan this range are usable. In certain embodiments, the inorganic postlayer 84 may comprise silicon nitride (SiN_(x)) or SiO₂, although a widevariety of other materials may be used, some of which are discussed ingreater detail below. In FIG. 11E, the inorganic post layer 84 ispatterned and etched to form inorganic posts 88. It can be seen in FIG.11E that the edges of the inorganic posts 88 preferably taper which,like the tapered or sloped sidewalls of the apertures 86, facilitatecontinuous and conformal deposition of overlying layers. It can be seenthat the post structure 88 in the illustrated embodiment has a thicknesswhich is thinner than that of the sacrificial layer 82, and comprises asubstantially flat base portion 89, a sloped sidewall portion 87, and asubstantially horizontal wing portion 85 which extends over a portion ofthe sacrificial material. Thus, the post 88 advantageously provides asubstantially flat surface at the edge of the post for supporting anoverlying movable layer 66 (See FIG. 11G), minimizing stress and theresultant undesired deflection which might occur if the movable layer 66were deposited over a less flat edge.

In one embodiment, the inorganic post layer 84 and resultant post 88comprise diamond-like carbon (DLC). In addition to being extremely hardand stiff (roughly 10× harder than SiO₂), the DLC inorganic post layer84 can be etched with an O₂ dry etch. Advantageously, an O₂ dry etch ishighly selective relative to a wide variety of sacrificial materials,including but not limited to Mo and a—Si sacrificial material, as wellas other sacrificial materials discussed above. An inorganic postcomprising DLC thus provides a very stiff post, lessening the likelihoodand amount of downward flexure of the edges of the support post 88 whenoverlying moving or mechanical layers are pulled downward during MEMSoperation, while permitting the use of an etch which is relativelybenign to a wide variety of materials.

In FIG. 11F, a highly reflective layer 90 is deposited over theinorganic posts 88 and the exposed portions of the sacrificial layer 82.A mechanical layer 92 is then deposited over the highly reflective layer90. For convenience, as noted above, the highly reflective layer 90 andthe mechanical layer 92 may be referred to and depicted in subsequentfigures as a movable layer 66 (see FIG. 11G), or more particularly as adeformable reflective layer whenever the mechanical layer 92 isdeposited directly over the highly reflective layer 90. In alternateembodiments, the movable layer 66 may comprise a single layer which hasthe desired optical and mechanical properties. For example, mechanicalor moving layers for MEMS mechanical switches need not includereflective layers. In still further embodiments, as already discussed,the movable layer may comprise a mechanical layer and a reflective layerwhich are substantially separated, such as layers 14 and 34 of FIG. 7C.An exemplary process for forming such a MEMS device having partiallyseparated mechanical and reflective layers is discussed in greaterdetail below with respect to FIGS. 35A-35H and 36A-36C. In FIG. 11G, arelease etch is performed to selectively remove the sacrificial layer82, forming an interferometric modulator element 60 having aninterferometric gap 19 through which the movable layer 66 can be movedin order to change the color reflected by the interferometric modulatorelement 60. Prior to the release etch, the movable layer 66 ispreferably patterned to form columns (not shown), and may advantageouslybe further patterned to form etch holes (see, e.g., etch holes 100 inFIG. 9J) which facilitate access to the sacrificial layer by the releaseetch.

In an alternate embodiment (as described below with respect to FIG. 17),the reflective layer may be deposited prior to the deposition andetching of the support layer 84, such that the reflective layer willunderlie the support structure 88 in the finished modulator element.

In yet another embodiment, support structures may be formed both aboveand below the movable layer 66. FIGS. 12A-12D depict such an embodiment,which includes the steps of FIGS. 11A-11F. In FIG. 12A, it can be seenthat once the reflective layer 90 and the mechanical layer 92 have beendeposited over the underlying support structure 88, a rivet layer 96 isdeposited over the mechanical layer 92.

Subsequently, as seen in FIG. 12B, the rivet layer 96 is patterned andetched to form support structures 62 located above the mechanical layer92. In certain embodiments, the same mask used in the steps of FIG. 11Eto pattern the underlying support structures 88 may be used to patternthe overlying support structures 62. FIG. 12C depicts the patterning andetching of the mechanical layer 92 and the reflective layer 90 to formetch holes 100 in those layers, exposing the sacrificial layer 82.

Finally, as shown in FIG. 12D, the sacrificial layer 82 is etched toremove the sacrificial material and release the interferometricmodulator, permitting movement of movable layer 66 through theinterferometric gap 19. Thus, an interferometric modulator displayelement has been formed, wherein support structures 62 and 88 sandwichportions of the movable layer 66 in the depression originally defined bythe aperture 86 (FIG. 11C), providing additional support and rigidity,and in certain embodiments, permitting the use of the upper supportstructures 62 for other purposes (e.g., see FIG. 7E and attendantdescription), as discussed above.

In other embodiments, it may be desirable to provide an underlying rigidsupport structure having a substantially flat upper surface. One processfor fabricating one such embodiment of an interferometric modulator isdescribed with respect to FIGS. 13A-13E. This process includes the stepsof FIGS. 11A-11D. In FIG. 13A, it can be seen that a layer ofphotoresist material 134 is deposited over the layer of rigid supportmaterial 84 in order to form a mask, which will be used to etch thesupport material 84 to form support structures 88, as discussed abovewith respect to FIG. 11D. It can be seen that the deposited photoresistmaterial 134 is thick enough to extend above the level of the rigidsupport layer 84, completely filling depressions 136 in the supportlayer 84 corresponding to the underlying tapered apertures 86 (FIG.11B).

In FIG. 13B, the photoresist material 134 has been patterned to form amask 140, and the mask has been used to etch the underlying rigidsupport layer 84, forming support structures 88. In FIG. 13C, thephotoresist material of the mask has been etched back such that theremaining photoresist material 134 is located within the depressions 136in the support structures 88. In FIG. 13D, a reflective layer 90 and amechanical layer 92 are deposited over the top of the support structures88, including the remaining photoresist material 134, forming a movablelayer 66. As can be seen, the use of the remaining photoresist material134 forms a substantially flat or planar surface on which the componentsof the movable layer 66 may be deposited, as compared to the embodimentshown in FIG. 11G. The rigidity of the support structures is alsoincreased by the additional material within the depression. In FIG. 13E,etch holes 100 have been formed in the movable layer 66, and a releaseetch has been performed to remove the sacrificial layer 82, therebyreleasing the interferometric modulator element 60.

In alternate embodiments, the photoresist mask used to form the supportstructures 88 may be completely removed, and a filler material fillingthe cavities 136 of the support structures 88 may be deposited in aseparate step, which may have the advantage of providing a stiffer rivetmaterial, such as spin-on dielectric. In such an embodiment, anysuitable material may be utilized, including but not limited toplanarization materials discussed above. However, the process discussedwith respect to FIGS. 13A-13E advantageously minimizes the stepsrequired to fabricate such a modulator element by eliminating theseparate deposition of an additional layer. In yet further embodiments,a rigid support structure similar to the rigid support structures 62 ofFIG. 9J and other embodiments may additionally be formed over themovable layer 66 of FIG. 13E, in order to provide additional support.

FIGS. 14A-14C illustrate one set of alternative steps which may beperformed to ensure that the reflective layer 90 will not underlie thebase of the support structure. These steps may be performed, forexample, after the steps of FIG. 9A-9D. In FIG. 14A, it can be seen thata reflective layer 90 is deposited over the unetched sacrificial layer82. In FIG. 14B, it can be see that both the reflective layer 90 and theunderlying sacrificial layer 82 have been patterned and etched to formtapered apertures 116. In FIG. 14C, a mechanical layer 92 is depositedover the etched sacrificial and reflective layers 82 and 90. Unlike thetapered apertures 86 of FIG. 9E, it can be seen that the side walls ofthe tapered apertures 116 will not be coated with the reflective layer90 (see FIG. 9F), but are rather coated with the mechanical layer 92,such that the mechanical layer 92 is in contact with the underlyingdielectric layer 78. It will be understood that an interferometricmodulator element may be fabricated by, in one embodiment, subsequentlyperforming the steps described with respect to FIGS. 9G-9J, includingformation of a rivet structure.

FIGS. 15A-15C illustrate another series of alternative steps which maybe used to eliminate those portions of the reflective layer which willunderlie the base of the support structure to be formed. These steps maybe performed after the steps of FIGS. 9A-9E. Once the sacrificial layer82 has been patterned and etched to form tapered apertures 86, areflective layer 90 is deposited over the sacrificial layer 82, as shownin FIG. 15A. In FIG. 15B, the reflective layer 90 is patterned andetched to remove at least the portions of the reflective layer that arein contact with the underlying dielectric layer 78. In furtherembodiments, the portions of the reflective layer 90 in contact with theside walls of the tapered aperture 86 may also be removed. In FIG. 15C,it can be seen that a mechanical layer 92 is deposited over the etchedsacrificial and reflective layers 82 and 90. Subsequently, the stepsdescribed with respect to FIGS. 9G-9J may be performed in order tofabricate an interferometric modulator element including a rivetstructure.

With reference to FIG. 16A, in certain embodiments comprising a poststructure, an etch barrier layer 130 is provided which protects thesacrificial layer 82 during the etching of the inorganic post layer 84(see FIG. 11D) to form the inorganic posts 88 (See FIG. 16B). In theillustrated embodiment, the etch barrier layer 130 is deposited over thesacrificial layer 82 prior to patterning and etching to form the taperedapertures 86 (e.g., between the steps of FIG. 9D and FIG. 9E). The etchbarrier layer 130 is then patterned and etched either prior to or at thesame time as the forming of the tapered apertures 86 (e.g., may bedeposited and patterned in the same manner as the reflective layer ofFIGS. 14A-14C). As can be seen in FIG. 16A, the etch barrier layer 130covers only the portion of the sacrificial layer 82 away from thetapered aperture 86. Advantageously, patterning and etching the etchbarrier layer 130 separately from (e.g., prior to) etching thesacrificial layer 82 permits greater control over the etching of theetch barrier 130, preventing the barrier 130 from overhanging theaperture 86 due to the aperture etch undercutting the etch barrier 130.Such an undercut would negatively affect the continuous and conformaldeposition of the post layer 84 (see FIG. 11D). Examples of suitableetch barriers include, but are not limited to, Al, Al₂O₃, Cr, and Ni. Incertain embodiments, as discussed in greater detail below with respectto FIGS. 17A-17B, a reflective layer may advantageously serve as an etchbarrier layer 130.

The inorganic post layer is then deposited, and etched to form theinorganic posts 88, as seen in FIG. 16B. As can be seen, the sacrificiallayer 82 has not been exposed to the etching process which forms theposts, as the mask used to protect the inorganic post layer 84 anddefine the post structures 88 during the etching process protects thepost layer overlying the tapered aperture 86, and the etch barrier layer130, which now extends between the inorganic posts 88, protect thoseportions of the sacrificial layer 82. Because of the etch barrier 130,an etch can be used to form the support post 88 which is nonselectivebetween the inorganic post and the sacrificial layer. This isparticularly advantageous with respect to dry etches, such as etchesinvolving chemistries such as SF₆/O₂, CHF₃/O₂, CF₄/O₂, NF₃/O₂ and allother fluorine-containing chemistry, but is also useful with respect towet etches. As discussed in greater detail, below, in certainembodiments the etch barrier layer 130 may advantageously remain in thefinished device.

With reference to FIGS. 17A and 17B, in an alternate embodiment, an etchbarrier layer 130 is deposited after the sacrificial layer 82 has beenpatterned and etched to form the tapered apertures 86, such that itcoats the walls and base of the tapered apertures 86. The inorganic postlayer is then deposited above the etch barrier layer 130 and patternedand etched to form posts 88, as depicted in FIG. 17A. As can be seen inFIGS. 17A and 17B, this etch barrier layer 130 underlies the entireinorganic post 88, in addition to protecting the sacrificial layer 82not covered by the inorganic post 88.

As can be seen in FIG. 17B, which depicts the modulator section of FIG.17A after the release etch has been performed, the upper portion of theinorganic post 88 is protected by the mechanical layer 92 deposited overthe inorganic post 88. Thus, the inorganic post 88 is completelyenclosed by the combination of the etch barrier layer 130 and themechanical layer 92 during the release etch. Because it is completelyenclosed, etch chemistries which are nonselective with respect to theinorganic post material and the sacrificial material may be used in boththe inorganic post etch and the release etch. In a particularembodiment, the same material may be used as both the sacrificialmaterial 82 and the inorganic post material which forms post 88, due tothe isolation of each layer from the etch performed on the other layer.

In the embodiment depicted in FIG. 17B, that portion of the etch barrierlayer 130 which extends beyond the patterned inorganic post 88 mayremain in the finished interferometric modulator, or may be removed atsome point during the fabrication process, as described with respect toFIGS. 18 and 19, below. In one embodiment, the etch barrier layer 130may comprise aluminum or another highly reflective material capable ofserving as an etch barrier layer. In this embodiment, the etch barrierlayer 130 may be left in the finished modulator to serve as thereflective surface in a deformable reflective layer. In such anembodiment, only the mechanical layer 92 need be deposited over theinorganic post 88 and the etch barrier layer 130, as the reflectivematerial comprising the etch barrier layer 130 will deform along withthe mechanical layer 92. In another embodiment, the etch barrier layermay comprise a substantially transparent material, such as a thin layerof Al₂O₃. In interferometric modulators or other optical MEMS elementsof this type, an additional reflective layer (not shown), is preferablydeposited prior to deposition of the mechanical layer 92, in order toform a deformable reflective layer such as movable layer 66 of FIG. 11G.

In one particular embodiment, the etch barrier layer 130 comprises Al,and is resistant to a fluorine-based etch. In another embodiment, whichis particularly suitable for use when the sacrificial layer comprisesa—Si, rather than Mo, the etch barrier layer comprises Al or Al₂O₃, andmay alternately comprise Ti or W. Other suitable etch barrier materialsinclude, but are not limited to, Cr and Ni. In one embodiment, the etchbarrier layer is between 40 and 500 Angstroms, but may be either thickeror thinner, depending on the embodiment. In an embodiment in which theetch barrier layer 130 comprises a conductive material, removal of theconductive layers within the optical stack 16 in the area directlyunderlying the support structure 88 advantageously minimizes the risk ofa short between the conductive etch barrier layer and the conductivelayers within the optical stack 16 (see, e.g., FIG. 9B and attendantdescription).

In an alternate embodiment, described with respect to FIG. 18, an etchbarrier layer 130 may be deposited, and an overlying post structure 88formed, as described with respect to FIG. 17A. After the overlying poststructure 88 is formed, a patterning and etching process may be used toremove those portions of the etch barrier layer 130 located away fromthe post structure 88, such that the remaining portions of the etchbarrier layer 130 remain underneath the post structure 88, protecting itfrom the subsequent release etch. Advantageously, because the portionsof the etch barrier layer not underlying or very close to the supportpost have been removed, the optically active portions of the display aresubstantially unaffected by the etch barrier layer. Thus, thecomposition and thickness of the etch barrier layer may be selectedpurely on the basis of the desired level of protection from the releaseetch, without regard for the opacity of the etch barrier layer.

In a further refinement of the above process, described with respect toFIG. 19, it can be seen that depending on the composition of the poststructure 88, the exposed portions of the etch barrier layer 130 may beetched without the need for an additional patterning process, using thepost structure 88 itself as a hard mask during the etching of the etchbarrier layer 130. Advantageously, the remaining portion of the etchbarrier layer 130 is substantially flush with the edge of the poststructure 88, such that no more of the etch barrier layer 130 is leftthan is necessary to protect the post structure 88 from the releaseetch, even further minimizing optical effects of the etch stop 130.

With respect to FIG. 20, in an embodiment in which a support structureis formed adjacent to a movable layer 66, such as the illustrated rivetstructure 62 overlying the movable layer 66, it may be desirable toprovide for additional adhesion to secure the support structure 62 tothe movable layer. In particular, because the actuation of theinterferometric modulator will tend to pull the movable layer 66 in adirection away from the overlying support structure 62, improvedadhesion between the movable layer 66 and the overlying supportstructure 62 will minimize the risk that the movable layer 66 will beginto pull away from the rivet 62. In the illustrated embodiment, after thedeposition of the mechanical layer 92 (see FIG. 9F), an adhesionenhancement layer 136 may be deposited. As shown, the adhesionenhancement layer 136 has been deposited after deposition of themechanical layer and prior to patterning of the rivet layer, which aresimultaneously patterned to form the rivet structure 62.

In another embodiment in which support structures such as poststructures 88 of FIG. 11E are formed prior to deposition of the movablelayer, an adhesion enhancement layer may be formed over the post layer84 (see FIG. 11D) prior to patterning the post layer 84 to form supportposts 88 (see FIG. 11E). However, it will be understood that theadhesion enhancement layer may alternately be deposited and patternedafter the formation of support structure 88, such that the adhesionenhancement layer overlies the tapered edges of the support post 88,enhancing the efficacy of the adhesion enhancement layer but adding tothe complexity of the process by adding separate mask and etch steps.

These adhesion enhancement layers may comprise any of a wide variety ofmaterials based on the composition of the movable layer and the layersforming the support structures, as certain materials may providedifferent amounts of adhesion enhancement when in contact with differentmaterials. One example of an adhesion enhancement material which isuseful in conjunction with a wide variety of mechanical and rivetmaterials is Cr, but many other materials may be used as adhesionenhancement layers.

As discussed above, modifications may be made to a fabrication processin order to protect a deposited rivet structure from the release etch.Advantageously, this both permits the use of a wider range of materialsin the rivet structure, as the sacrificial material need not beselectively etchable relative to the rivet material if the rivetmaterial is not exposed to the release etch, and minimizes any damagewhich might be caused to the rivet structure if it was exposed to therelease etch.

In one embodiment, described with respect to FIG. 21, it can be seenthat a rivet structure 62 has been formed over a mechanical or movinglayer, which in the illustrated embodiment is a reflective movable layer66, which extends over a patterned sacrificial layer 82. The rivet 62 isthen covered with a protective layer 104, which will remain over therivet 62 at least until the release etch has been performed, at whichpoint it may or may not be removed. In one embodiment, the protectivelayer 104 comprises a layer of photoresist material. In anotherembodiment, a distinct layer of an alternate etch barrier material formsthe protective layer 104. The protective layer 104 may be any materialsufficiently resistant to the release etch to provide the desired levelof protection for the rivet. In one embodiment, for example, the rivet62 may comprise SiN_(x), the release etch may be a XeF₂ etch, and theprotective layer 104 may comprise a layer of photoresist materialdeposited after the rivet 104 has been formed.

In another embodiment, the stability of a rivet structure may beincreased through the securing or anchoring of the rivet structure tostructures underlying the mechanical layer or the deformable reflectivelayer. In one embodiment, depicted in FIG. 22, the movable layer 66(which may comprise a mechanical layer 92 and a reflective layer 90, seeFIG. 9J) is deposited over the patterned sacrificial layer 82 such thatit takes the shape of the tapered apertures 86. The movable layer 66 isthen etched at least a portion of the base of the tapered aperture 86 soas to expose an underlying layer, which in this case is the dielectriclayer at the top of the optical stack 16. The rivet layer is thendeposited as discussed above and patterned to form the rivet structure62. As can be seen, the rivet structure 62 now extends through anaperture 106 extending through the substantially flat base portion 99 ofthe movable layer 66, securing the rivet structure 62 to the underlyingoptical stack 16, advantageously providing additional stability to therivet structure, both because the adhesion of the rivet material to theunderlying dielectric layer may be better than the adhesion to themechanical layer 92 and because the rivet structure 62 no longer relieson the adhesion between the movable layer 66 and the optical stack 16 tohold the rivet structure 62 in place. It will also be understood that inalternate embodiments, the rivet structure 62 may be secured to astructure other than the upper surface of optical stack 16. Forinstance, in an alternate embodiment (not shown) in which the rivetstructure 62 and a post structure underlying the movable layer 66sandwich a portion of the movable layer 66, the rivet structure can besecured to the underlying post structure through an aperture in themovable layer 66, or to any underlying layer with better adhesion, suchas, in certain embodiments, the reflective layer 90 of the movable layer66.

In another process, described with respect to FIGS. 23A-23E, a platingprocess can be used to form inorganic post structures. This processincludes the steps of FIGS. 9A-9E. In FIG. 23A, it can be seen that athin seed layer 208 is deposited over the patterned sacrificial layer82. In one embodiment, the seed layer 208 comprises a thin layer ofcopper and can be formed by sputtering or CVD. In another embodiment,the seed layer may comprise aluminum, and may serve as the reflectivelayer in an optical MEMS device by omitting the removal step describedbelow with respect to FIG. 23E. In FIG. 23B, a mask 202 is formed overthe seed layer 208, having an aperture 210 which defines the shape ofthe post to be formed by the plating process. It can be seen that theedges of the illustrated aperture 210 have a reentrant profile oroverhang (also referred to herein as a negative angle), such that thepost structure to be formed will have a taper which corresponds to thetapered edges of the aperture 210. In FIG. 23C, it can be seen that aplating process is used to form a layer 212 of post material. In FIG.23D, the mask 202 is removed, leaving only the seed layer 208 and thepost layer 212. Next, in FIG. 23E, the portions of the seed layer 208located away from the post layer 212 are etched away (e.g., using thepost layer 212 as a mask for this etch), forming an inorganic post 214comprising the remaining portions of the seed layer 208 and the postlayer 212. Subsequently, a mechanical or deformable reflective layer canbe deposited over the post, which is facilitated by the tapered angle atedge of the post wings. As discussed above, in an embodiment in whichthe seed layer comprises aluminum or another reflective material, theremoval step of FIG. 23E may be omitted from the process, and amechanical layer may be deposited over the reflective seed layer.

Metal which has been anodized to form metal oxide can also be used toform support structures. In one embodiment, discussed with respect toFIGS. 24A-24B, anodized aluminum or Ta is utilized in the formation ofan inorganic post. In FIG. 24A, it can be seen that a metallic layer254, which may be Al or Ta, is formed over a patterned sacrificial layer82. In FIG. 24B, the layer 254 has been patterned to form the shape ofthe inorganic posts, and has been anodized to form Al₂O₃ or Ta₂O₅inorganic posts 256. Advantageously, anodized Al₂O₃ or Ta₂O₅ forms adielectric layer which is free from pinhole defects, greatly reducingthe chance of a short between the mechanical layer deposited thereoverand the optical stack 16.

As discussed above, it is easier to consistently and conformally depositrivet material over a tapered aperture. However, because of the taperedshape, certain rivet structures may be susceptible to downwarddeflection of the edges of the rivet structures, particularly inembodiments in which the rivet layer is thin relative to the mechanicallayer. In certain embodiments, it may be desirable to provide additionalunderlying support for a rivet structure, in order to constrain suchdownward deflection of the edges of the rivet structure. FIGS. 25A-25Hand FIG. 26 illustrate embodiments in which additional support may beprovided through modification of a support structure.

In one embodiment, described with respect to FIGS. 25A-25H, sacrificialmaterial which is protected from the release etch may be utilized toprovide additional support to the rivet structure. This process forfabricating an interferometric modulator element comprising suchsupports includes the steps described with respect to FIGS. 9A-9D. InFIG. 25A, the sacrificial layer 82 is patterned and etched to removeannular sections 120 of sacrificial material, leaving columns 122 ofsacrificial material separated from the remainder of the sacrificiallayer 82.

In FIG. 25B, protective material 124 is deposited such that it fillsannular sections 120. As can be seen, the protective material preferablycompletely fills the annular sections 120. Advantageously, the materialcomprising the sacrificial layer 82 is selectively etchable relative tothe protective material 124, which may be, for example, a polymericmaterial or a photoresist material. Advantageously, the protectivematerial 124 may comprise a self-planarizing material, such asspin-on-dielectric, so as to facilitate filling the annular section 120,and so as to provide a planar surface for the subsequent deposition ofan overlying movable layer. However, depending on the size of theannular structure 120 and the method used to deposit the protectivematerial 124, a variety of materials may be suitable for use as theprotective material 124. In FIG. 25C, it can be seen that the protectivematerial has been etched back to the level of the sacrificial layer 82,such that the upper surface of the isolated columns 122 of sacrificialmaterial is exposed.

In FIG. 25D, a second patterning and etching process is utilized to formtapered apertures 126 within the isolated columns 122 of sacrificialmaterial. In FIG. 25E, a reflective layer 90 and a mechanical layer 92are deposited over the sacrificial material, followed by the depositionof a rivet layer 96 over the mechanical layer. It will be understoodthat variations in the fabrication process as discussed above mayadvantageously be used to remove the portion of the reflective layer 90which will underlie the support post, as depicted in FIG. 25E.

In FIG. 25F, the rivet layer 96 is etched to form support structures 62,and the mechanical layer 92 and reflective layer 90 are subsequentlypatterned and etched to form etch holes 100 and optionally also toseparate strips of the movable layer 66, as shown in FIG. 8. Thus, FIG.25F shows an unreleased MEMS device. In FIG. 25G, a release etch isperformed to remove those portions of the sacrificial layer 82 notenclosed by the annular sheaths of protective material 124 (e.g., thecolumns 122). At this point, an interferometric modulator element 60 isformed having rivet structures 62 overlying the movable layer 66, andcolumns 122 of unetched sacrificial material surrounded by sheaths ofprotective material 124 located underneath and around the depressions inthe movable layer 66. Optionally, the sheath of protective material 124may be removed by a subsequent step, through, for example, an ashing oretching process, resulting in an interferometric modulator comprisingposts of exposed, but unetched, sacrificial material, as seen in FIG.25H.

In yet another embodiment, desired supplemental support for rivetsupport structures such as 62 may be provided through use of the samematerial used to form the rivet structures. In one embodiment, describedwith respect to FIGS. 26A-26E, an alternate support post and rivetstructure is formed from a spin-on material. In FIG. 26A, it can be seenthat a layer of sacrificial material 82 has been deposited and patternedto form tapered apertures 86, and a movable layer 66 has been depositedover the patterned sacrificial material 82. In FIG. 26B, holes 140 havebeen patterned in the movable layer 66, and the sacrificial material 82is etched to form vias 142 which extend, in this embodiment, from theholes 140 to the underlying optical stack 16. FIG. 26C depicts anoverhead view of this area at this point in the fabrication process, inwhich it can be seen that multiple vias 142 surround the depressioncorresponding to the tapered aperture 86. Any number or shape of thevias may be utilized, and the tapered aperture 86 may take multiplepossible shapes. In FIG. 26D, a layer 146 of spin-on material isdeposited. The spin-on material, or other self-planarizing material,will flow to fill the vias 142. In this embodiment, the spin-on materialfills the tapered aperture 86, and flows through the holes 140 to fillthe vias 142. Finally, in FIG. 26E, it can be seen that the spin-onmaterial is cured and patterned to remove the spin-on material locatedaway from the tapered aperture 86 and the vias 142, forming a supportstructure 150 which comprises a rivet-like upper portion and post-likestructures or legs 152 extending from the rivet-like portion through themovable layer 66 to the optical stack 16. The sacrificial layer 82 (seeFIG. 26D) has also been removed by a release etch to form aninterferometric gap 19. Advantageously, the legs 152 lend stability tothe support structure, such that the sloped portion of the mechanicallayer is not so easily pulled down into the cavity beneath it duringoperation, and the adhesion between the rivet and the mechanical layeris thereby enhanced. The rivet structure 150 is also adhered to theunderlying optical stack, anchoring the rivet structure in place.

It will be understood that variations can be made to the above processflow. In certain embodiments, the holes 140 may be formed in theportions of the movable layer 66 overlying the sidewalls of the taperedaperture 86. In other embodiments, the cavities 142 need not be verticalcavities, as depicted in FIG. 26B, but may extend in a diagonaldirection, or may not extend all the way through the sacrificial layerto the optical stack 16. For example, the holes 140 may be formed in themovable layer 66 in the sidewalls of the apertures 86, and the cavities142 may extend in a diagonal direction down to the optical stack 16.FIG. 27 illustrates such an embodiment, in which overlying supportstructures 150 comprise legs 152 which extend at an angle through holesin the tapered portion of the movable layer 66. Such an angled etch maybe performed, in one embodiment, through the use of a reactive ion etch(RIE), although other suitable techniques may also be used. In certainembodiments, the support structures 150 may comprise discrete legs 152,as shown in FIGS. 26E and 27, or may comprise a continuous annularsupport structure.

Various other methods may be used to form support structures and othercomponents of the interferometric modulator. In certain embodiments, aplating process can be utilized to form component of an interferometricmodulator such as rivet and post support structures. FIGS. 28A-28Billustrate a portion of a process for utilizing a plating process toform a rivet structure 160. This process includes the steps of FIGS.9A-9F. In FIG. 28A, it can be seen that a mask 162, which may be aphotoresist mask in certain embodiments, is deposited over the movablelayer 66, and patterned to form an aperture 164 which will define theshape of the desired rivet structure. In FIG. 28B, it can be seen that aplating process has been used to form a rivet structure 160 within theaperture 164. In one embodiment, the plating process is anelectroplating process. In various embodiments, the rivet 160 maycomprise materials included, but not limited to, nickel, copper, andgold, but any material that can be plated and is preferably notsusceptible to the release etch may be used.

In addition to forming the various components of the interferometricmodulators, the layers deposited in the fabrication processes discussedherein can also be used to form other components within or connected toan array of interferometric modulator elements. FIG. 29 depicts aportion of an interferometric modulator element in which a movable layer66 forms a strip electrode 170, and a conductive layer such as aconductive layer 72 within the optical stack 16 (see FIG. 9A) forms asecond strip electrode 172 which runs beneath and perpendicular to thefirst strip electrode 170. It can also be seen that multiple supportstructures may be provided across the length of the strip electrode 170,such as rivet structures 62. The first, or upper, strip electrode 170 iselectrically connected to a conductive interconnect or lead 174, whichmay in turn be electrically connected to a landing pad or connectionpoint 176, at which an electrical connection may be made with anexternal component, such as a bump. Similarly, the second, or lower,strip electrode 172 is electrically connected to a lead 178 and aconnection point 180. The first strip electrode 170, which may also bereferred to as a column electrode (although it will be understood thatthe designation of the upper electrode as the column electrode isarbitrary and depends simply on the orientation of the MEMS array), isgenerally spaced apart from the substrate by an air gap orinterferometric cavity within the array, although it will be understoodthat at various locations within the array (e.g., at the supportregions), no air gap may exist between the column electrode 170 and thesubstrate. The second strip electrode 172, which may also be referred toas a row electrode, is generally fabricated either directly on thesubstrate, or if there are intervening layers, such that nointerferometric gap exists between the second strip electrode 172 andthe substrate).

In certain embodiments in which the lead 178 and the connection point180 are formed from ITO with no overlying layers, a connection may bemade directly between an external device and the connection point 180.However, the high resistivity and contact resistance with ITO may makesuch an embodiment undesirable. In another embodiment, a layer ofconductive material, such as the material which forms the movable layer66, may be deposited over the ITO for most of the length of theconnection point 180 and lead 178, in order to reduce the resistance ofthat portion of the structure. However, in certain embodiments in whichthe mechanical layer comprises a deformable reflective layer formed fromtwo layers (e.g., a mechanical layer 92 and reflective layer 90, as canbe seen in FIG. 9F), contact resistance between certain of those layersmay have an undesirable effect on the resistance of the lead 178,particularly when one of those layers is aluminum, which has poorcontact resistance in contact with an ITO layer.

Advantageously, a conductive material may be deposited over the ITOlayer which has desirable contact resistance in contact with the ITOlayer. FIGS. 30A and 30B depict steps in such a fabrication process,showing cross-sections taken along line 30-30 of FIG. 29. In FIG. 30A,it can be seen that at a stage in the fabrication process prior to thedeposition of the mechanical layer (e.g., a stage corresponding to FIG.9E or earlier), only a layer 72 of ITO has been deposited at this area(or any overlying layers, such as partially reflective layer 74 of FIG.9A, have been selectively removed). In FIG. 30B, however, the mechanicallayer 92 has been deposited not only over the layers in the area wherethe interferometric modulator element is to be formed, but also over theconnection point 180 (not shown) and the lead 178, and thus directlyoverlies the ITO layer 72. It can also be see that the reflective layer90 (see FIG. 9E) has either not been deposited over the ITO layer 72, orhas been selectively removed after deposition and prior to thedeposition of mechanical layer 92. In one embodiment, the reflectivelayer 90 (see FIG. 9E) is deposited over the lead 178 and connectionpoint 180, but patterned and etched to remove those portions of thereflective layer prior to the deposition of the mechanical layer 92. Inone embodiment, the mechanical layer comprises Ni, which has favorablecontact resistance in contact with ITO. The mechanical layer 92 is thenpatterned and etched to remove the portions of the layer not overlyingthe lead 178 or connection point 180, as seen in FIG. 30B. Also, as canbe seen with respect to FIG. 29, the mechanical layer (shown as shaded)is preferably also removed at the edge of the lead close to the array,to avoid shorting the strip electrodes 170 and 172 to one another.

Thus, in one embodiment, the mechanical layer is utilized as aconductive layer in contact with the ITO leads and connection points. Inanother embodiment in which the rivet material comprises a conductivematerial, the rivet material can instead be deposited over the ITO andused to form the conductive layer over the ITO, in place of themechanical layer 92 of FIGS. 30A-30B. In a particular embodiment therivet layer comprises Ni. Advantageously, this embodiment does notinvolve patterning and etching one portion of a deformable reflectivelayer (the reflective layer) separately from the other portion (themechanical layer).

In a particular embodiment, the mechanical layer 92 comprises Ni, whichhas desirable resistance and contact resistance properties, but a widevariety of mechanical layer materials may be used. In anotherembodiment, the ITO layer need not extend all the way through the lead178 to the connection point 180. Rather, the deposited mechanical layer92 may alone form the connection point 180 and a large portion of thelead 178. In addition to lowering the resistance and contact resistanceof these components, the deposition of the mechanical layer 92 alsoadvantageously increases the height of these components, facilitatingconnections between external components.

Similarly, the mechanical layer 92 may form the lead 174 and theconnection point 176. In one embodiment, there is no need for the lead174 or connection point 176, which are in connection with columnelectrode 170, to comprise any ITO, and the mechanical layer 92 mayextend the entire length of the lead 174 in order to form a connectionbetween the lead 174 and the strip electrode 170. This is because thecolumn electrode 170 is separated from the substrate, unlike the rowelectrode 172 which is formed on the substrate (e.g., a patterned stripof ITO).

Because the row and column leads would otherwise be exposed, and thusvulnerable to shorting and other damage which may occur due toenvironmental or mechanical interference, it may be desirable to deposita passivation layer over the exposed row and column leads 174 and 178.In a particular embodiment, the same material which is used to form therivet structure 62 can be utilized to passivate the leads 174, 178,protecting them from external electrical or mechanical interference.Such an embodiment is described with respect to FIGS. 31A-31D. In FIG.31A, which is a cross section of a partially fabricated lead 174 of FIG.29 taken along the line 31-31 in accordance with a different embodiment,it can be seen that the mechanical layer 92 has been deposited, but notyet etched. In FIG. 31B, it can be seen that the layer 96 of rivetmaterial has been deposited (as seen in, for example, FIG. 9G), and thislayer of rivet material has also been deposited over the mechanicallayer 92 located outside the array of interferometric modulators. InFIG. 31C, it can be seen that the layer of rivet material has beenpatterned (as seen in FIG. 9H), and that the layer of rivet material hassimultaneously been patterned to form a strip 182 which will overlie thelead 304. Finally, in FIG. 31D, the mechanical layer has been patternedto separate the strip electrode 170 from the surrounding electrodes (andto form any necessary etch holes in the strip electrode), and issimultaneously patterned to form the lead 174. In an alternateembodiment, the mechanical layer may be patterned and etched at the sametime as the rivet layer. It will be understood that this rivet layer iseither not deposited over the connection point 180, or is etched toremove the portion of the rivet layer which covers the connection point180, in order to permit a connection to be made with an externalcomponent. It will also be understood that if the lead 178 (see FIG. 19)in connection with the row electrode is passivated in accordance withthe above process, the resultant lead 178 may comprise a layer of ITO 72underlying the mechanical layer 92.

In yet another embodiment, the mechanical layer 92 may be patternedprior to the deposition of the rivet layer, forming the lead 174 andseparating the strip electrode 170 from the neighboring stripelectrodes. Thus, the rivet layer may be subsequently patterned so as tocover not only the upper portion of the lead 174, but also to protectthe sides, as can be seen in FIG. 32, which depicts a lead 174fabricated by this process viewed along the line 31-31 of FIG. 19.Advantageously, this further protects the lead 174. In otherembodiments, passivation material may be deposited over the leads in aprocess distinct from the deposition of the support structure layer. Insuch a process, any suitable dialectic layer may be used to passivatethe lead, and need not be suitable for use as a support structure layer.For example, any suitable dielectric layer used in the fabrication ofthe MEMS device, such as for example the dielectric layer within theoptical stack or a dialectic layer used as an etch stop layer, may beused to passivate a lead.

In certain embodiments, it may be desirable to provide a movable layer66 having varying stiffness over different parts of an MEMS element, orto more easily provide an array of MEMS elements wherein adjacentelements comprise movable layers having differing stiffness. Forexample, a modulator element in which the movable layer has differentactuation voltages in different areas can be used to create grayscale,as differing amounts of the modulator elements can be actuated bymodifying the applied voltage, as the actuation voltage will vary acrossthe array of modulator elements. In other embodiments, additionalstiffness may be desirable in areas which have less support, such asaround the edges of the modulator element. One method of fabricating aninterferometric modulator element having such a varying stiffness isdescribed with respect to FIGS. 23A-23B and comprises the steps of FIGS.9A-9G.

In FIG. 33A, it can be seen that the rivet layer, which in thisembodiment may comprise silicon oxide, has been etched to form supportstructures 62, as described with respect to FIG. 9H. However, theembodiment of FIG. 33A differs from that of 9H, in that additionalpatches, or ribs, 190 of the rivet material have been left unetched. InFIG. 33B, it can be seen that the fabrication process is completed asdiscussed with respect to FIGS. 9I and 9J, resulting in aninterferometric modulator element 60 (viewed along the line 33B-33B ofFIG. 34) having support structures 62 and ribs 190 overlying portions ofthe movable layer 66. A top view of the interferometric modulatorelement 60 of FIG. 33B having residual ribs 190 comprising rivetmaterial is depicted in FIG. 24.

As discussed above, these residual ribs 190 may inhibit deformation ofthe movable layer 66 in the area surrounding the patch, such that thatsection of the movable layer 66 will require a higher actuation voltage.They may also be used to provide additional support to the mechanicalarea near the edges of the movable layer. In certain embodiments, themovable layer 66 may be susceptible to undesired curling or flexure.This may be particularly problematic at those areas of the movable layer66 close to the gaps 65 between the strip electrodes of the movablelayer 66. The placement of such ribs 190 may control this undesiredflexure, so as to ensure that the height of the interferometric gap 19(see FIG. 23B) remains more constant across an interferometricmodulator. In addition, as the positioning of these ribs structures 190affects the stiffness of the movable layer 66 in the surrounding area,these rib structures 190 may be used to modify the actuation voltagerequired to move the MEMS device into an actuated state. This may bedone, for instance, to normalize the actuation voltage across theelement, or alternately to provide a differing actuation voltage acrossthe MEMS element, such as to provide grayscale, as discussed above.

In a further embodiment, the rivet layer which is etched to form supportstructures 62 and residual rib structures 190 may comprise anelectroactive material, such as a piezoelectric material. Through theapplication of electroactive material to the upper surface of themechanical layer 92 in the form of ribs 190, the behavior of the movablelayer 66 can be further controlled. The application of electroactivematerial can, for instance, be used to modify the voltage applied at agiven location in the modulator element.

As discussed above, the methods and structures discussed above may beused in conjunction with an optical MEMS device having a movable layercomprising a reflective layer which is partially detached from amechanical layer. FIGS. 35A-35H illustrate an exemplary process forforming support posts underlying a portion of the movable layer in sucha MEMS device, which in the illustrated embodiment is an interferometricmodulator. This process may include, for example, the steps describedwith respect to FIGS. 9A-9D, in which an optical stack is deposited, anda sacrificial layer is deposited over the optical stack.

In FIG. 35A, it can be seen that a reflective layer 90 is deposited overthe sacrificial layer 82. In certain embodiments, the reflective layer90 may comprise a single layer of reflective material. In otherembodiments, the reflective layer 90 may comprise a thin layer ofreflective material with a layer of more rigid material (not shown)overlying the thin layer of sacrificial material. As the reflectivelayer of this embodiment will be partially detatched from an overlyingmechanical layer, the reflective layer 90 preferably has sufficientrigidity to remain in a substantially flat position relative to theoptical stack 16 even when partially detached, and the inclusion of astiffening layer on the side of the reflective layer located away fromthe optical stack can be used to provide the desired rigidity.

In FIG. 35B, the reflective layer 90 of FIG. 35A is patterned to form apatterned mirror layer 220. In one embodiment, the patterned mirrorlayer 220 comprises a contiguous layer in which apertures correspondingto the locations of (but wider or narrower than) support structures havebeen formed. In another embodiment, the patterned mirror layer 220 maycomprise multiple reflective sections detatched from one another.

In FIG. 35C, a second sacrificial layer 226 is deposited over thepatterned mirror layer 220. Preferably, the second sacrificial layer 226is formed from the same material as the first sacrificial layer 82, oris etchable selectively with respect to surrounding materials by thesame etch as the first sacrificial layer 82. In FIG. 35D, taperedapertures 86 are formed which extend through both the second sacrificiallayer 226 and the first sacrificial layer 82.

In FIG. 35E, a layer of post material 84 has been deposited over thepatterned sacrificial layers 92 and 226, such that it coats the sides ofthe apertures 86, as described with respect to FIG. 11D. In FIG. 35F,the layer of post material has been patterned to form post structures88, as described with respect to FIG. 11E. The patterned post structures88 may overlap with the edges of the mirror layer 220. It can also beseen in FIG. 35E that an aperture 228 has been formed in a portion ofthe second sacrificial layer 196 overlying the patterned mirror layer220, exposing at least a portion of the patterned mirror layer 220.

In FIG. 35G, a mechanical layer 92 is deposited over the posts 88 andthe exposed portions of the second sacrificial layer 226 and thepatterned mirror layer 220. IN particular, it can be seen that themechanical layer 92 at least partially fills the aperture 198 (see FIG.35F), such that a connector portion 222 connecting the mechanical layer92 and the patterned mirror layer 220 is formed.

In FIG. 35H, a release etch is performed which removes both the firstsacrificial layer 82 and the second sacrificial layer 226, therebyforming an interferometric gap 19 between the patterned mirror layer 220and the optical stack. Thus, an optical MEMS device is formed, whichincludes a movable layer 66 comprising a mechanical layer 92 from whicha patterned mirror layer 220 is suspended, where the patterned mirrorlayer 220 is partially detached from the mechanical layer 92. Thisoptical MEMS device, may be, for example, an interferometric modulatorsuch as that described with respect to FIG. 7C and elsewhere throughoutthe application. In non-optical MEMS, the suspended upper electrode neednot be reflective.

It will be understood that the above process may be modified to includeany of the methods and structures discussed above. In particular, itwill be seen that the above process may be modified to include theformation of a rivet structure, either instead of or in conjunction withthe formation of a post structure. In particular, in an embodiment inwhich only rivet structures are formed, the above process may be furthersimplified by forming the tapered apertures at the same time as theaperture overlying a portion of the mirror layer in which the connectingportion will be formed. In another embodiment in which a rivet layer isdeposited, only a very thin layer of conductive material may bedeposited in a step equivalent to that of FIG. 35G, and a laterdeposited rivet layer (which can be dielectric) may be patterned andetched to serve the mechanical function of the mechanical layer, withthe thin layer of conductive material serving the conductive function.

In a further embodiment, the same material which forms the poststructures may be used to form stiffening portions on the upper surfaceof a detached mirror layer 200. FIG. 36A-36C illustrate such anembodiment, which includes the steps of FIGS. 35A-35C. In FIG. 36A, itcan be seen that at the same time as the tapered apertures 86 areformed, additional apertures 230 have been formed over the patternedmirror layer 220, exposing portions of the patterned mirror layer 220.In certain embodiments, these apertures 230 may advantageously take theform of grooves extending near edges of the patterned movable layer 220,however a wide variety of shapes, including annular or substantiallyannular shapes, may be suitable.

In FIG. 36B, it can be seen that a layer of post material 84 has beendeposited such that it not only coats the edges of the tapered apertures86, but also is deposited over the exposed portions of the patternedmirror layer 220 within the additional apertures 230. In FIG. 36C, itcan be seen that the fabrication process has proceeded in a similarfashion to that described with respect to FIGS. 35F-35H, and that areleased interferometric modulator has been formed. In particular, itcan be seen that the patterned mirror layer 220 comprises stiffeningstructures 232 (e.g., annular rings) on the upper surface of thepatterned mirror layer 220, formed from the same material as the posts88. It can also be seen that the portion of the mechanical layer 92overlying the stiffening structures 232 has been removed to formapertures 234. It will be understood that because the mirror layer 220has been partially detached from the mechanical layer 92, the mechanicallayer 92 need not comprise a continuous layer of material, but mayinstead comprise, for instance, strips of mechanical material extendingbetween connector portions 222 and support structures such as posts 88.Thus, portions of the mechanical layer may be removed by the samepatterning step that forms mechanical strips (see FIG. 8), as depictedin FIG. 36C, in order to ensure that no connection remains between thestiffening structures 232 and the overlying mechanical layer 92.

It will be understood that various combinations of the above embodimentsare possible. For instance, in certain embodiments, certain of thesupport structures disclosed herein may be used in conjunction withother support structures disclosed herein, as well as other suitablesupport structures not discussed in this application. Variouscombinations of the support structures discussed above are contemplatedand are within the scope of the invention. In addition, it will beunderstood that support structures formed by any of the methods abovemay be utilized in combination with other methods of forming supportstructures, in order to improve the rigidity and durability of thosesupport structures.

It will also be recognized that the order of layers and the materialsforming those layers in the above embodiments are merely exemplary.Moreover, in some embodiments, other layers, not shown, may be depositedand processed to form portions of an interferometric modulator elementor to form other structures on the substrate. In other embodiments,these layers may be formed using alternative deposition, patterning, andetching materials and processes, may be deposited in a different order,or composed of different materials, as would be known to one of skill inthe art.

It is also to be recognized that, depending on the embodiment, the actsor events of any methods described herein can be performed in othersequences, may be added, merged, or left out altogether (e.g., not allacts or events are necessary for the practice of the methods), unlessthe text specifically and clearly states otherwise.

While the above detailed description has shown, described, and pointedout novel features of the invention as applied to various embodiments,it will be understood that various omissions, substitutions, and changesin the form and details of the device of process illustrated may be madeby those skilled in the art without departing from the spirit of theinvention. As will be recognized, the present invention may be embodiedwithin a form that does not provide all of the features and benefits setforth herein, as some features may be used or practiced separately fromothers.

1. A method of fabricating an electromechanical device, comprising:providing a substrate; depositing an electrode layer over the substrate;depositing a sacrificial layer over the electrode layer; patterning thesacrificial layer to form apertures; depositing a conductive movablelayer over the sacrificial layer; forming support structures overlyingthe movable layer and at least partially within apertures in thesacrificial layer, wherein the support structures extend over only aportion of the conductive movable layer; and etching the sacrificiallayer to remove the sacrificial layer, thereby forming a cavity betweenthe movable layer and the electrode layer.
 2. The method of claim 1,wherein the movable layer includes a mechanical sublayer and areflective sublayer.
 3. The method of claim 2, wherein the mechanicalsublayer is formed directly over the reflective sublayer.
 4. The methodof claim 2, wherein depositing the movable layer over the sacrificiallayer comprises: depositing a reflective sublayer over the sacrificiallayer; patterning the reflective sublayer; depositing a secondsacrificial layer after and over the reflective sublayer; and depositinga mechanical sublayer after and over the reflective sublayer.
 5. Themethod of claim 2, wherein the reflective sublayer comprises aluminum.6. The method of claim 2, wherein the movable sublayer comprises atleast one material selected from the group of: nickel and chromium. 7.The method of claim 2, wherein the reflective sublayer is depositedafter the patterning of the sacrificial material, additionallycomprising removing at least a portion of the reflective layer locatedalong a base of the apertures in the sacrificial layer
 8. The method ofclaim 2, wherein the reflective sublayer is deposited prior to thepatterning of the sacrificial material.
 9. The method of claim 1,wherein the support structures comprise at least one material selectedfrom the group of: aluminum, AlO_(x), silicon oxide, SiN_(x), nickel,and chromium.
 10. The method of claim 1, wherein forming the supportstructures comprises: depositing a layer of support material over themovable layer and at least partially within the apertures in thesacrificial layer; and patterning the layer of support material to formsupport structures located over the apertures.
 11. The method of claim10, additionally comprising: patterning the sacrificial layer to formannular holes, forming columns of sacrificial material; and depositing alayer of protective material over the sacrificial material, filling theannular holes with the layer of protective material, wherein thesacrificial material is selectively etchable relative to the protectivematerial.
 12. The method of claim 11, additionally comprising etchingback the layer of protective material to expose the sacrificial layer,wherein said etching back is done prior to patterning the sacrificiallayers to form apertures, and wherein said apertures are formed withinthe columns of sacrificial material.
 13. The method of claim 12,additionally comprising removing the protective material to expose sidesof the columns of sacrificial material, wherein the protective materialis removed after the sacrificial layer has been etched to form thecavity
 14. The method of claim 10, additionally comprising: forming atleast one aperture in the movable layer; and etching a via through thesacrificial material extending from the at least one aperture in themovable layer to a layer underlying the sacrificial material, whereinthe layer of support material fills the via.
 15. The method of claim 14,wherein the layer of support material comprises a planarizing material.16. The method of claim 14, wherein the at least one aperture in themovable layer is formed through a substantially horizontal portion ofthe movable layer.
 17. The method of claim 14, wherein the movable layercomprises sidewalls within the aperture, and wherein the at least oneaperture is formed through a sidewall of the movable layer.
 18. Themethod of claim 10, wherein patterning the support layer to form atleast one support structure further comprises patterning the supportlayer to form at least one rib structure located over the movable layerand away from the apertures in the sacrificial material.
 19. The methodof claim 10, additionally comprising polishing the support layer toreduce the height of the support structure.
 20. The method of claim 10,wherein patterning the layer of support material comprises etching thesupport layer selectively relative to the movable layer.
 21. The methodof claim 10, wherein the movable layer comprises a substantially flatbase portion, additionally comprising etching an aperture through atleast a portion of the substantially flat base portion prior todepositing the layer of support material.
 22. The method of claim 1,wherein forming the support structures comprises: depositing a mask overthe movable layer; patterning the mask to define at least one aperture,wherein the aperture is located over one of the apertures in thesacrificial layer; and forming at least one support structure within theaperture in the mask by a plating process.
 23. The method of claim 22,wherein the support structure is formed by an electroplating process.24. The method of claim 1, wherein depositing the electrode layer overthe substrate comprises: depositing a layer of ITO over the substrate;and depositing a layer of chromium over the layer of ITO.
 25. The methodof claim 1, additionally comprising depositing a partially reflectivelayer over the electrode layer, wherein the movable layer includes amechanical sublayer and a reflective sublayer, the reflective sublayerlocated on the side of the movable layer facing the partially reflectivelayer.
 26. The method of claim 1, additionally comprising patterning theelectrode layer to form electrode apertures, wherein said electrodeapertures are located underneath the apertures in the sacrificial layer.27. The method of claim 1, additionally comprising depositing adielectric layer between the electrode layer and the sacrificialmaterial.
 28. The method of claim 27, wherein the dielectric layercomprises silicon oxide.
 29. The method of claim 1, additionallycomprising depositing an adhesion enhancement layer over the movablelayer prior to formation of the support structures.
 30. The method ofclaim 1, additionally comprising depositing a protective layer over thesupport structure prior to etching the sacrificial material.
 31. Themethod of claim 1, additionally comprising patterning the movable layerto form etch holes prior to etching the sacrificial layer.
 32. Themethod of claim 1, additionally comprising forming a first lead inelectrical connection with the movable layer, and a second lead inelectrical connection with the electrode layer.
 33. The method of claim32, wherein forming the movable layer comprises depositing at least amechanical layer.
 34. The method of claim 33, wherein forming the firstlead comprises depositing the mechanical layer on a portion of thesubstrate extending away from a portion of the mechanical layeroverlying the sacrificial layer, and patterning the mechanical layer toform the first lead.
 35. The method of claim 33, wherein forming thesecond lead comprises depositing the mechanical layer over an exposedportion of the electrode layer, and patterning the mechanical layer toform the second lead and to electrically isolate the second lead from aportion of the movable layer overlying the sacrificial material.
 36. Themethod of claim 35, wherein the electrode layer comprises ITO and themechanical layer comprises nickel, and wherein the nickel is depositeddirectly over an exposed portion of the ITO.
 37. The method of claim 32,wherein forming the support structures comprises depositing a layer ofsupport material, the support material comprising a non-conductivematerial, and wherein the layer of support material is deposited over atleast one of said first and second leads, and remains over at least aportion of said lead to protect said lead.
 38. The method of claim 37,wherein the layer of support material is deposited prior to patterningsaid at least one of said first and second leads.
 39. The method ofclaim 37, wherein the layer of support material is deposited afterpatterning said at least one of said first and second leads.